China's Minister of Railways Liu Zhijun has been placed under investigation "for serious disciplinary violations", the state-run Xinhua news agency says.
It gave no details, but in the past similar language has been used to refer to allegations of corruption.
Mr Liu was also replaced as the ministry's Communist Party secretary.
He had been minister since 2003, leading an ongoing multi-billion dollar investment programme in China's railway network.
He has not publicly commented on the allegations against him.
Last year, China publicly admitted in a report that its corruption problem was "still very serious", setting out new measures to tackle it.
The report said that more than 200,000 cases - including embezzlement and bribery - had been investigated since 2003.
The document was released after the introduction of new rules requiring members of the governing Communist Party to report incomes and investments.
However, critics say corruption is ingrained in the system and new regulations will not solve the problem.