The 66-year-old man from Fond du Lac, Wisconsin, was southbound on Montana Highway 83 just after 9:30 a.m. Sunday when a bear crossed the tree-lined highway in front of him, the Montana Highway Patrol said.
The man was unable to avoid hitting the bear and was thrown from the motorcycle. The man, who was not wearing a helmet, died at the scene south of the town of Swan Lake, the patrol said.
His name has not been made public.
State game wardens found the injured bear and killed it, Trooper James Hawkins said.