Ministerial-level officials in China are rarely targeted in corruption crackdowns, and the investigation of Liu Zhijun could be especially damaging to the party's credibility. The government has made huge investments in high-speed rail projects, and the railway system is vital to moving people and goods across the vast country.
Liu, 58, who has been head of the railway ministry since 2003, has been removed from his position as the ministry's Communist Party chief, the Xinhua News Agency reported late Saturday. He will be replaced by Sheng Guangzu, 62, head of the General Administration of Customs.
Liu is being investigated by the Communist Party's corruption watchdog, which can remove him from his party post but not from his government job. However, in cases like this, government officials almost always follow the party's lead, and Liu is likely to be stripped of his minister title.
The country's leadership has been trying to stamp out corruption - a major source of public distrust and anger - with President Hu Jintao saying in a speech to the party's graft watchdog earlier this year that the situation is "grave" and will require long-term efforts.
Last year, China punished 146,517 officials for corruption, Xinhua said. Among them were 5,098 officials at the county level or higher.
The government has launched numerous anti-graft campaigns in recent years. Some have seen judges and high-profile party figures sentenced to years in prison. Others have brought down some of China's top corruption hunters, who were found to be lining their own pockets.
There were no details about alleged wrongdoing by Liu, and the announcement of the probe was unexpected.
"Liu Zhijun allegedly committed severe violations of discipline. At present, it is being investigated," Xinhua's report said.
The central government's website posted a story as recently as Feb. 6 about Liu visiting a train station in the southern hub of Guangzhou, meeting with local railway officials and riding on a fast train.
Hong Kong media have said that Liu's brother is Liu Zhixiang, a former railway ministry official brought down by corruption and handed a suspended death sentence.
Liu Zhixiang, the deputy chief of the railway bureau in central China's Wuhan city, was convicted in 2006 of charges including embezzlement and taking bribes, the government-run China Court website said. He was also found to have hired thugs to beat up a man with whom he was having a business dispute.
Associated Press researcher Henry Hou contributed to this report.