"I think he'd be terrific. If we did run into problems in markets, I think he'd actually be the best person you could have in the job," Buffett said.
CNNMoney reported Tuesday Dimon is known as President Obama's favorite bank executive.
Working against him as a contender for Geithner's job Dimon's opposition to the Dodd-Frank Act, much of which he would have to implement as head of the Treasury Department.
In addition, JPMorgan Chase lost $5.8 billion in May in a much-publicized trading fiasco.
But Buffett argued that the bank's trading losses should not block Dimon's chances of becoming secretary of the Treasury.
Geithner is expected to announce his departure soon. He previously said he did not want to stay past Obama's first term in office.