Metro Transit spokesman Bob Gibbons said the driver was assaulted by six to eight teenagers on Robert Street between 4th and 5th Streets as his bus was arriving downtown.
Gibbons said the driver called the operations center at about 9:20 p.m. and asked for help because he had "a group of kids acting up on the bus." He called back later a short time later to report that he had been attacked.
The driver was taken to Regions Hospital in St. Paul.
The bus was on Route 68, which runs primarily on Robert Street south of downtown, Gibbons said.
No arrests have been reported as of early today.