Asked if he was committed to the sanctions during his Senate Finance Committee confirmation hearing, Mnuchin said "100% so," CNBC reported.
"The president-elect has made it very clear that he would only change those sanctions if he got, quote, a better deal and we would get something in return," Mnuchin told senators.
The White House has taken action against Russia in response to its 2014 annexation of Crimea and most recently after suspected Russian efforts to influence the 2016 U.S. election. The Treasury has a role in enforcing sanctions.
President-elect Donald Trump has promised better relations with Russia and at times praised President Vladimir Putin. He recently said he would consider dropping sanctions in exchange for a move like a nuclear drawdown.
Trump's comments and his choice of Rex Tillerson, who has Russia ties, as secretary of State have raised questions about his willingness to enforce the sanctions.
Some senators have called for even more measures against Russia.