Firefighters put out four separate fires on a six miles stretch of U.S. Highway 12 between Lavina and Roundup Wednesday night.
It happened around 5 p.m. between Lavina and Dean Creek Road.
Crews were mop-up around 8:30 p.m.
The saddle bags on a motorcycle caught on fire, according to Golden Valley County Undersheriff Mark Olson.
The motorcycle was heading east and saddle bag fires sparked the grass fires in the ditch on the south side of the highway.
The fires burned about 125 acres.
Olson said the man on the motorcycle suffered severely burned hands.
He was taken to the hospital in Roundup and then to Billings.
No structures were threatened.
Fire departments responded from Lavina, Ryegate, Broadview, Laurel, Billings, Bull Mountain and Dean Creek.
Sheriff's deputies from Golden Valley, Wheatland and Musselshell counties and the Montana Highway Patrol responded.