The White House says Obama and Xi spoke yesterday, the same day the UN Security Council unanimously endorsed the deal.
China is a permanent member of the Security Council and was part of the group of five Security Council members plus the EU that negotiated the deal with Iran.
The Security Council resolution also approved a provision to automatically reinstate sanctions if Iran cheats. The US had been concerned China or Russia might be reluctant to go along.
The White House says Obama and Xi agreed cooperation between the US and China is critical to the deal's implementation.