The 36-year-old and a female companion were sledging at Fideris in the canton of Graubünden when they came across the bus, which was transporting other tobogganers up to the start of the run, said cantonal police.
The driver brought the bus to a halt immediately, but the two on the sledge were unable to stop and collided head-on with the front of the bus.
The man suffered unspecified injuries and was flown by Rega air rescue service to hospital in Chur.
The woman was unhurt.
It's the second sledging accident in the past ten days after a woman died when her sledge plunged off the edge of the piste on to rail tracks near Andermatt.