Xu Wanping, 44, was convicted of "incitement to subvert state power" and sentenced on Friday in a closed-door hearing by a court in southwest China's Chongqing municipality, where he lives, Chen Xianying, his wife said.
Chen said she did not find out about the court's decision until later. "He's innocent," she said. "They should release him immediately."
Xu was among about eight political dissidents who were known to have been arrested in May, a month after large anti-Japanese demonstrations occurred in several large Chinese cities.
The detentions of the dissidents reflect China's unease with anti-Japanese sentiments and fear that dissidents critical of the government could take advantage of the protests to influence ordinary people to protest against other issues, such as corruption and lack of freedoms.
Xu is believed to be the first of the group of dissidents to be sentenced.
During three weekends in April, tens of thousands of demonstrators across several Chinese cities, including Beijing and Shanghai, threw stones, eggs and bottles at the Japanese embassy, shops and restaurants.
Protesters opposed Japan's recent approval of history textbooks that China and other Asian countries say gloss over its wartime atrocities, and Japan's attempt to secure a permanent seat on the United Nations Security Council.