"As one of the influential websites in China, Sina has failed to shoulder its due responsibility and we feel deeply sorry for that," the company, which runs Weibo akin to Twitter with over 300 million users said in a statement to state-run Xinhua news agency.
China heavily police the Internet for content deemed politically subversive or indecent. Social networking sites such as Twitter and Facebook are blocked in the country fearing social instability.
The Internet market in the country has more than 500 million users and has grown to become world's biggest.
Authorities last week announced to revoke the Sina's two crucial licenses on Internet publication and audio and video dissemination and imposed "a large number of fines" for pornography on its website.
China has shut down 110 websites as part of a national crackdown on online pornography, the State Internet Information Office said.
Some 3,300 accounts on China-based social networking services, such as WeChat and Sina Weibo, as well as online forums have been deleted in the recently launched Cleaning the Web 2014 campaign, according to a Xinhua report.
Weibo is widely seen as revolutionising highly regulated social media networking which in turn put immense pressure challenging the monopoly of the state media.
The National Office Against Pornographic and Illegal Publications said that 20 articles and four videos posted on Sina.com were confirmed to have contained lewd and pornographic content following "a huge amount" of public tip-offs.
Sina on the same day posted an apology to netizens and the public.
"We would like to make another apology to express our deep regret to the public," the statement today said.
Sina will carefully observe the authorities' decision and will follow strict standard in supervising its contents, it said.
It also encouraged the netizens and the public to report violations on its website and published a hotline number and an Email address to receive such tip-offs.
"Sina is willing to work with other website operators to make vigorous efforts in the country's anti-porn campaign and create a clean Internet environment," the statement said.