State media had said that the junior high school student, surnamed Yang, was the first person detained under strict new rules to tackle what the government calls the spread of online rumours.
The release of the 16-year-old in the western province of Gansu represents a victory for many microbloggers, who protested online after his detention last Tuesday for comments on his Twitter-like microblog.
Yang had said that a man described by police as having committed suicide had been murdered instead.
Police said the man committed suicide by jumping from a high-rise building on September 12, after a visit to a karaoke club and that Yang's "phony" posts had prompted some residents to stage a protest.
Yang had served a week-long detention for "administrative infractions", the official Xinhua news agency said on Monday. He was initially detained on a charge of "provoking trouble".
"In light of Yang being a teenager, his active compliance with the investigation, his sincere regret for the crime and the circumstances of being a minor, local police withdrew the criminal case and handed down a lenient punishment," Xinhua said.
China's top court and prosecutor said in early September that people would be charged with defamation if online rumours they created were visited by 5,000 Internet users or reposted more than 500 times.
The move was seen as a government effort to rein in online social media, increasingly used by Internet users to discuss politics, despite stringent censorship.
© Thomson Reuters 2013
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