I found Carios kelleyi Cooley & Kohls (formerly Ornithodoros kelleyi) (Acari: Ixodida: Argasidae) on five species of bats (Eptesicus fuscus, Myotis lucifugus, Myotis ciliolabrum, Myotis evotis, and Myotis volans) in the prairies of southeastern Alberta and north central Montana. This is the first occurrence of ticks on bats in Canada. This is also the first record of C. kelleyi on M. evotis and M. volans. Dates of parasitization ranged from 22 May to 17 October, and the number of ticks per host ranged from 1 to 44 (median two ticks per host). Number of parasitized individuals was significantly higher in rock-roosting E. fuscus compared with building-roosting E. fuscus, rock- and building-roosting M. lucifugus, and rock-roosting M. ciliolabrum and M. evotis. A significant sex bias was noted in rock-roosting E. fuscus in 2000 with significantly more females parasitized. The number of ticks per bat host was highest in 2001, corresponding to the driest and hottest summer of the survey.