The incident took place on Sunday near Ali al-Salim Air Base, 70km northwest of the capital Kuwait City, US military spokesman Captain Randall Baucom said on Tuesday.
"Four of the soldiers were taken to a Kuwaiti armed forces hospital and are in a stable condition, while 21 were treated at a local camp," Baucom added.
He said Kuwaiti police were questioning the bus driver, a Kenyan national. He did not elaborate.
The bus, which was leased from a local company, was driving along a highway to the base when the accident happened, Baucom said.
News of the accident broke only on Tuesday when the local newspaper Al-Anba reported it with Kuwaiti sources.
Kuwait has been a major ally of Washington in the region, since a US-led coalition fought the 1991 Gulf War that ousted occupying Iraqi forces.
The small oil-rich state was the launchpad for the invasion of Iraq that toppled Saddam Hussein in April.