We report on 1153 winter prey items eaten by 11 Barred Owls (Strix varia) from 6 areas in west-central Montana. Small mammals dominated the diet, representing 98 to 100% of the frequency of prey eaten by each owl. Of the small mammals, voles (Microtus) were clearly the most numerous prey group, representing 97.6% of all prey. Within Microtus, the Montane Vole (Microtus montanus) was the most numerous species eaten at 5 areas, and the Meadow Vole (M. pennsylvanicus) was the most numerous species eaten at 1 area. Pellet length × width for 4 Barred Owls averaged 61.4 × 24.5 mm. Because of the adaptability of Barred Owls and the overlap of their range with that of the Spotted Owl (S. occidentalis) in the northwestern United States, future dietary comparisons between seasons may also help elucidate the comparative ecology of these congeners as conservation issues arise.