It happened near West 1st Avenue and Broadway around 10 p.m.
Fire crews say the two men suffered 2nd and 3rd degree burns and were taken to University of Colorado Hospital.
The explosion caused structural damage to the garage and may have to be torn down.
The cause of the explosion is not known, but fire crews say it doesn't appear to be suspicious at this time.
(KUSA-TV © 2013 Multimedia Holdings Corporation)