The mayor of the eastern Chinese city of Nanjing is the latest target in the Communist Party's high-profile crackdown on official corruption.
A party statement released on Thursday said Ji Jianye is under investigation for severe violations of discipline and law, which usually refers to graft.
The People's Daily, the party's official mouthpiece, reported that Ji was known to award lucrative development contracts to friends. It said the case against him may have involved $3.2 million.
Several low-level officials and a handful of more senior leaders have been taken down in the anti-graft drive by President Xi Jinping. President Xi has warned that failure to deal with widespread corruption within party ranks could bring the end of the party's grip on power.
Investigations against government officials are conducted internally and usually last several months. In almost every case, they end with the accused being found guilty.
Last month, ex-Politburo member Bo Xilai was convicted of bribery, embezzlement and abuse of power in a scandal that also saw his wife convicted of murdering a British businessman.
Bo, the highest-profile leader brought down by the anti-corruption campaign, is appealing the conviction.