The trial was the first since the mid-March riots. The massive anti-government protests in Lhasa on March 14 were the largest challenge to Chinese rule in the Himalayan region in nearly two decades.
Three men received life sentences, including a Buddhist monk, the official Xinhua News Agency said. The monk allegedly led 10 people, including five other monks, to destroy local government offices, burn down shops and attack policemen, Xinhua said.
Of the five other monks, two were sentenced to 20 years and three to 15 years in prison.
"It's impossible to say whether these are fair trials or not," Cheng Hai, a Beijing lawyer, told the Washington Post. Hai was one of several lawyers who offered their services as criminal defense lawyers to the accused. "I don't know if they received enough legal assistance," Hai said.
China has said 22 people died in the riots, while Tibet's government-in-exile announced Tuesday that it believes at least 203 Tibetans were killed in the ensuing crackdown. The Associated Press said it was impossible to independently verify the information because access to Tibet and surrounding provinces has been closed to foreigners since the unrest.
China's response to the riots has drawn attention to the government's human rights record and other policies, as the communist country prepares to host the Olympic Games in August.
On Wednesday, Beijing marks the 100-day countdown to the Olympics with songs, a mass run and even prayers, hoping to put behind it the tumultuous events of the past month which have taken much gloss off its preparations.
Human rights groups and pro-Tibetan supporters have protested against the Olympic torch relay at several stops around the world, causing massive disruptions in some cities.
Two pro-Tibet activists who planned to protest at Hong Kong's leg of the Beijing Olympics torch relay were stopped when they arrived at the territory's airport Tuesday, and one was immediately put on a return flight to New York, activists told the AP.
The Olympic torch had been making its way through tightened security in Vietnam, where it's on its final international leg. Hundreds of flag-waving supporters cheered as the relay began in downtown Ho Chi Minh City. Security along the route was tight and there were no immediate signs of protesters.
Earlier in Hanoi, police detained several people for unfurling a banner and shouting "Boycott the Beijing Olympics."