Chen Guangcheng, a blind human rights activist, was sentenced to four years and three months in prison by a court in east China's Shandong province on Thursday, the Xinhua news agency announced.
Chen's chief lawyer, Xu Zhiyong - who was barred from attending the half-day trial on Friday last week - said: "This is completely unreasonable and against the law.
"This definitely affects China's image and its claims as a country ruled by law."
Chen's family members say that the charges of damaging property and disrupting traffic were trumped up and his wife was shocked by the sentence.
"I thought they were going to sentence him even though he's innocent, but I never expected such a heavy sentence," Yuan Weijing, who was not informed of the sentence by the court, told Reuters.
Chen ran into trouble with authorities in Shandong's Linyi city last year after accusing them of forcing many women to be sterilised and have abortions as late as eight months into their pregnancy.
China's population control policy that has been in place for 25 years is aimed at restricting urban couples to having one child and rural parents to two.
The central government officially condones only economic sanctions against violators of the one-child policy, but human rights groups have long complained that much harsher penalties are regularly carried out.
"The trial was absurd, and now to have such a heavy sentence delivered this way is just unacceptable"
Xu Zhiyong, defence lawyer
Fellow human rights activists say Chen's sentence is indicative of a clampdown by officials on "rights defenders" - a growing network of lawyers, academics and dissidents seeking to expand citizens' freedoms through litigation and internet-driven campaigns for legal reform.
"This sentence was at the extreme of what anybody ever imagined", said Hu Jia, a Beijing dissident now under house arrest. "It's another attack on the rights defence movement, like the detention of Gao Zhisheng."
Gao, a human rights lawyer who has campaigned for the banned Falun Gong spiritual group, was detained by Beijing police after months of being followed by them.
Xu said he would appeal against Chen's sentence as "Chen Guangcheng is adamant that he's innocent. The trial was absurd, and now to have such a heavy sentence delivered this way is just unacceptable".
Xu and two other lawyers acting for the defence were detained on charges of theft as they prepared to defend Chen last week. At a hearing last month that was cancelled at the last minute, supporters of Chen said they were beaten by police and hired thugs.
Other Chinese rights activists who have campaigned for Chen's release have been put under house arrest in Beijing, deported from there to other cities, or have gone into hiding.