Microsoft is being probed in China apparently for antitrust in serious concern for the company's business in the country, which has been one of its largest markets.
Representatives from China's State Administration for Industry & Commerce made surprise visits to Microsoft offices in Beijing, Shanghai, Guangzhou and Chengdu, local media reported.
Microsoft later confirmed the development, but it did not say the reason for the investigation. The company said it would "actively cooperate" with the government.
However, news portal Sina reported quoting a source as saying that the investigation might have to do with antitrust matters.
The probe on Microsoft comes a few days after China's antitrust regulator said US chipmaker Qualcomm enjoys a monopoly in the world's second largest economy.
The National Development and Reform Commission (NDRC) is probing Qualcomm's Chinese subsidiary for allegedly overcharging and abusing its market position in wireless communication standards.
Under China's anti-monopoly law, the NDRC can impose fines of between 1% and 10% of a company's revenues for the preceding year. Qualcomm is expected to get more than $1bn (£587m, €743m) in fines.
The trade and political relations between the countries have recently been deteriorating over spying concerns, and both countries have targeted big companies especially in the technology sector.
In May, China's central government offices were banned from using Microsoft's latest operating system, Windows 8, after the US Justice Department charged five Chinese military members with hacking the systems of US companies to allegedly steal trade secrets.
US companies such as IBM and Cisco were reportedly closely monitored by China, after former US National Security Agency contractor Edward Snowden leaked top secret documents that revealed massive surveillance practices by the agency.
Foreign pharmaceutical companies operating in China have already been facing probes into alleged price fixing and bribery.
Meanwhile, the US is also targeting a number of prominent Chinese sectors and firms. It earlier accused telecom equipment maker Huawei of spying for Chinese government.
Recently, it imposed preliminary anti-dumping duties ranging from 26% to 165.04% on solar imports from China.