"The Committee to Protect Journalists (CPJ) condemns the Chinese authorities for censoring well-known blogger Zhao Jing, and is alarmed by Microsoft's agreement to pull down his site," the group said in a statement.
Zhao, whose on-line pen name is Michael Anti, had his site on Microsoft's China-based MSN Spaces hosting service deleted on December 30 after he wrote about the government's removal of top editors at the Beijing News newspaper.
His web logs also covered the strike by journalists at the paper in protest at the dismissals.
Microsoft deleted his website without prior notice after receiving a request from Chinese authorities, the committee said.
"China's growing attempt to stifle the free flow of news and opinion by making Internet companies complicit in their repressive policies is deeply disturbing," CPJ executive director Ann Cooper said.
"But for an Internet company to argue that it must honor contractual agreements when operating in China does not absolve it of its responsibility to uphold the ideal behind the Internet - the free and open exchange of information."
Microsoft last week defended its action, saying it was acting in line with local and global laws when it deleted the web log.
"Most countries have laws and practices that require companies providing online services to make the Internet safe for local users.
The article covered a strike
among staff at the Beijing News
Occasionally, as in China, local laws and practices require consideration of unique elements," the company said.
Microsoft had already faced intense criticism after it was revealed last year that its Chinese blogging service restricted the entry of sensitive terms such as "demonstration", "democratic movement" and "Taiwan independence".
The MSN Spaces operation, a Microsoft joint venture with state-owned Shanghai Alliance Entertainment, is the top blog hosting service in China.
The Chinese government has implemented a broad and sophisticated system of monitoring and censoring the Internet, where reporters and others often post news banned from publication elsewhere.
Fifteen of the 32 journalists in prison in China in 2005 were jailed for posting their writings on the Internet, the CPJ said.