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China has detained Chinese-born U.S. seismologist Youlin Chen for nearly two years and charged him with espionage over research connected to detecting North Korean nuclear tests, Reuters reported, citing his wife, U.S. lawmakers and hostage advocacy groups.
Chen, 54, was arrested by Chinese state security officers at Beijing International Airport on Nov. 5, 2024, as he prepared to return to Boston after visiting relatives and lecturing about his work at two universities, according to his wife, Yufang Rong, and hostage advocate Eric Lebson.
He was formally charged with espionage on May 1, 2025, but has not yet been brought to trial.
China’s Foreign Ministry rejected the U.S. characterization of the case, saying there was no so-called “wrongful detention” and that Chinese judicial agencies were handling the case in accordance with the law.
Chen became a U.S. citizen in 2011 and lives in Boston, Massachusetts.
U.S. Secretary of State Marco Rubio designated him as “wrongfully detained” on March 19, making efforts to secure his release a top U.S. priority, according to Reuters.
The Trump administration has not publicly announced the designation to preserve space for high-level diplomatic talks aimed at securing Chen’s freedom, Rong said.
A U.S. source familiar with the case told Reuters that the administration was “focused on gaining his release from his unjustifiable detention.”
The source reportedly spoke on condition of anonymity because of the sensitive nature of the diplomatic discussions.
Chen is the only American currently held in China who has been officially designated by Washington as wrongfully detained, according to his wife and hostage advocates.
Rong said White House and State Department officials told her that President Donald Trump raised her husband’s detention with Chinese President Xi Jinping during a state visit to Beijing in May.
Xi promised to look into the case, but the Chinese government has taken no action, she said.
The U.S. source did not directly confirm that Trump discussed Chen’s detention with Xi but told Reuters that the two leaders have a “very good personal relationship.”
“This is one of many facets in the U.S.-China relationship,” the source said. “No one issue is defining.”
Chen’s detention adds another point of tension between the nuclear-armed countries as Trump seeks to keep relations stable following last year’s trade war.
The case could arise again during a visit that Trump has said Xi will make to Washington in September.
In an interview with Reuters, Rong said she feared Chinese authorities had decided to convict her husband of espionage even before putting him on trial.
Espionage convictions in China can carry sentences of up to life imprisonment or the death penalty in cases considered especially serious.
“I believe they will convict him no matter what and the trial will be behind closed doors,” Rong said.
Rong is also a seismologist but does not collaborate on her husband’s research.
The Foley Foundation, a hostage advocacy organization tracking Chen’s case, believes he is among at least 12 Americans unjustly held in China, including people subject to exit bans, according to Elizabeth Richards, the group’s director of hostage advocacy.
Deputy White House Press Secretary Anna Kelly said Trump wanted all Americans detained abroad to return home.
“President Trump has been clear that he wants every American detained abroad to return home, and he has reunited over 100 individuals with their families since taking office this term,” Kelly said.
Chinese officials have interrogated Chen more than 100 times about his work on the seismographic signatures of North Korean nuclear tests, Rong told Reuters.
U.S. Embassy officials have visited him several times, but Chinese officials were always present, preventing him from speaking freely, she said.
Rong hired a Chinese lawyer, but the lawyer was allowed to meet Chen only after he had spent more than 13 months in detention.
Lebson, a former U.S. national security official whose hostage advocacy organization, Global Reach, is advising Chen’s family, said he believes China wants to use Chen’s expertise to improve its ability to conceal underground nuclear weapons tests through a technique called decoupling.
Lebson said that nuclear-testing experts consulted by his group had expressed similar concerns.
The technique involves detonating a device inside a large underground chamber to reduce the magnitude of the shock waves it produces.
The Trump administration accused China in February of attempting to conceal a low-yield underground nuclear test conducted on June 22, 2020, using the technique.
China has denied carrying out the test.
China and the U.S. have both signed but not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty.
Lebson said Chen works for a U.S. government contractor but has never held a U.S. security clearance or carried out classified work.
His research on seismic waves from North Korean nuclear test explosions was funded by the State Department and the Air Force Research Laboratory, according to Lebson.
The work was conducted in collaboration with Chinese academics, relied on publicly available Chinese data, and remains accessible online, he said.
A December 2020 paper by Chen reviewed by Reuters examined the magnitude of North Korea’s six known nuclear test explosions and methods for distinguishing their seismic signatures from those of earthquakes.
The cover page said the paper had been written for the State Department’s arms control bureau and was “approved for public release.”
Human rights organizations have argued that China’s state-secrets law gives authorities broad powers to retroactively classify publicly available information, including official statistics, as national security secrets.
Such action could potentially implicate people who possessed or shared information that had previously been openly available.
Rong told Reuters that Chen was subjected to “harsh conditions” at the beginning of his detention.
She said he was forced to sit on a hard stool throughout the day without being allowed to stand, read or exercise.
He was also unable to obtain medication for diabetes and other health problems, she said.
Rong said it had since become difficult to learn about the conditions of his confinement.
Chen has lost between 30 and 40 pounds, or about 13.6 to 18.1 kilograms, and receives insufficient food with little protein, fruit, or vegetables, she said.
She also said the medications provided to him were of poor quality.
U.S. Sen. Ed Markey, a Massachusetts Democrat, said he was “deeply concerned about Dr. Chen’s safety and well-being."
Markey led two other senators in a Dec. 17, 2025, letter urging Rubio to designate Chen as wrongfully detained.
“It is my hope that increased attention on his unjust detention will force the Chinese government to do the right thing and release Dr. Chen,” Markey said in a statement.
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