The move comes after the firing of a once high-flying official, who promoted Mao Zedong-era songs and stories.
Han Deqiang, founder of the leftist website Utopia, said police ordered that it be shut down because of content that criticized the Communist Party, its leaders and an upcoming party congress. The shutdown took effect Friday.
"I expected this to happen. If they want to shut us down, it is their right. We exercise our right to express ourselves, they exercise their right," Han said in a telephone interview.
Han is a vocal supporter of recently ousted Chongqing city Communist Party chief Bo Xilai, who strongly pushed a "Red Culture" campaign. The removal of Bo, considered a contender for a top job only months ago, was widely seen as a sign of divisive infighting.
Another prominent pro-Maoist website, Maoflag.net, also appeared to be shut down. The move appears to be part of wider censorship aimed at stifling discussion of Bo's downfall, the highest-level political sacking in years.
Bo's dismissal is yet to be fully explained, and came after a top aide fled temporarily to a US consulate, apparently to seek asylum and in violation of party rules. It also came as the senior leadership is gearing up for a handover of power to a younger generation of leaders in the fall, always a period of intense political bargaining.
Websites such as Utopia oppose privatization of the economy and other Western-style reforms, and have sometimes been critical of China's current leadership.
They also promote the achievements of Mao, who led a bloody two-decade revolution that ended with the establishment of Communist China in 1949, and held power until his death in 1976. His policies plunged the nation into years of famine, and led to the deaths of tens of millions.
China has sought to control political discourse following a flurry of rumours online about Bo's downfall, with authorities closing a dozen websites and detaining six people for circulating rumors of a coup that rattled Beijing.
In a further sign of such concerns, a military newspaper urged troops to ignore rumours and remain loyal to the Communist Party. The People's Liberation Army Daily said Friday in an editorial that troops should 'resolutely resist the incursion of all kinds of erroneous thoughts, not be disturbed by noises, not be affected by rumours, not be pushed by any undercurrent.''