The punitive measures were imposed on China Precision Machinery Import-Export Corporation (CPMIEC), according to a State Department notice posted in the Federal Register, a government gazette.
The notice did not identify the country to which alleged exports had gone and State Department spokesman Richard Boucher would not discuss specifics.
"They provided material contribution to a foreign country, which I can't name, in the area of missiles," he told reporters, adding though that the firm had been punished before for sales to Iran.
According to a study compiled by the Monterey Institute's Center for Nonproliferation Studies, CPMIEC has previously sent missile technology to Pakistan and Libya.
Based in Beijing, the firm is a unit of the China Aerospace Corporation (CASC).
The decision on sanctions came just days after a senior State Department official complained at gaps in China's non-proliferation policies, despite Beijing's promises to Washington to halt such exports.
"We continue to see problems in the proliferant behavior of certain Chinese entities and remain deeply concerned about the Chinese government's often narrow interpretation of nonproliferation commitments and lack of enforcement of nonproliferation regulations," said Paula DeSutter, assistant Secretary of State for verification and compliance.
"The Chinese Government appears to view missile nonproliferation, at least in part, not as a goal in and of itself but as an issue that needs merely to be managed as part of its overall bilateral relationship with the United States," she said in testimony to the US-China Economic and Security Review Commission on Thursday.
The sanctions, which are largely symbolic, prohibit the US government entering into contracts with the targeted firm, and prevent exports by that company into the United States.
They also empower the US government to suspend licences of any US entities exporting equipment to CPMIEC.
The sanctions will remain in force until Washington determines that it is in the US national interest to lift them or reliable evidence is provided that the offending sales have stopped, Boucher said.
The United States has previously imposed sanctions on CPMIEC in May 2002 and June 2003 for sales to Iran and in 1991 for violations of more general missile proliferation laws, he said.