"China always opposes any unilateral sanctions, especially when they harm the interests of a third party," Chinese Foreign Ministry spokesperson Lu Kang told media here.
Lu said that Beijing has lodged a protest with Washington as such sanctions are "not helpful" to promoting mutual trust and solving global issues.
The US on Friday imposed new sanctions after Iran conducted a ballistic missile test.
The sanctions affect 25 people and entities allegedly involved in Iran's ballistic missile programme or in supporting groups that the US considers terrorist.
The sanctions were imposed by President Donald Trump's administration two days after it had put Iran 'on notice' following the ballistic missile test.