Microsoft said Monday it was under investigation by antitrust authorities in China, pledging to cooperate in the investigation.
"We aim to build products that deliver the features, security and reliability customers expect, and we will address any concerns the government may have," Microsoft said in an emailed statement.
A source familiar with the matter said that some Microsoft offices in China have been raided as part of the investigation, but did not elaborate.
Media reports said earlier that Microsoft offices visited by China's State Administration for Industry and Commerce in Beijing, Shanghai, Guangzhou and Chengdu.
Foreign companies in China periodically draw scrutiny from regulators and state media.
Regulators have carried out aggressive probes into alleged corruption at foreign drug companies, including Britain's GlaxoSmithKline.
Microsoft, which is based in Redmond, Washington, said in May it would maintain efforts to gain approval in China for Windows 8 after Beijing announced a ban on the operating system on all new government computers.
News of the prohibition came amid a diplomatic row over an indictment in the United States of five members of a shadowy Chinese military unit for allegedly hacking US companies for trade secrets.