Yuan Keqin, a former professor at the Hokkaido University of Education, has been sentenced to six years in prison on espionage charges in China, sources said Wednesday.
Supporters have been demanding the Chinese scholar's early release, claiming he has been falsely accused.
A court in Changchun, Jilin Province, handed down the ruling in January, according to people familiar with the matter.
Yuan has already appealed the ruling.
He went missing in the city in May 2019 while temporarily returning to his homeland.
The Chinese Foreign Ministry later confirmed he had been detained and indicted for allegedly spying for a long time at the request of Japanese intelligence authorities.
Asked about Yuan's current conditions at a news conference in Beijing on Tuesday, Wang Wenbin, the ministry's spokesperson, only said that China is a country under the rule of law and handles the relevant case in accordance with the law.
Under the leadership of President Xi Jinping, the Chinese government is stepping up its antiespionage crackdown by strengthening the surveillance of foreign nationals and Chinese citizens who interact with non-Chinese nationals.
Other Chinese professors at Japanese universities have also disappeared after they temporarily returned home.