From Wired News:

Yahoo is stricter than any other search engine in China when enforcing censorship, said a journalism-advocacy group Thursday.

Paris-based Reporters Without Borders said their tests showed that Yahoo.cn blocked a higher percentage of politically sensitive results than Google.cn or the beta version of msn.cn.

The tests were performed using 10 politically-sensitive keywords like “press freedom” or “human rights” on the Chinese versions of Yahoo, Google and MSN, as well as a Chinese-based search engine, Baidu. [Full Text]

See also Yahoo! clear worst offender in censorship tests on search engines by Reporters Without Borders