Long-tailed weasels (Mustela frenata) are known to feed on mice and voles. However, in the Canadian Prairies, where Richardson's ground squirrels (Urocitellus richardsonii) are abundant (particularly during drought periods), long-tailed weasel predation on these medium-size rodents is poorly documented. In this study, predation by long-tailed weasels on Richardson's ground squirrels was documented from April 2008 to September 2008 in southwestern Saskatchewan during a drought period. I found that Richardson's ground squirrel remains were the dominant food item in percentage of occurrence, volume, and biomass from April to July. In August–September, however, deer mice (Peromyscus maniculatus) and insects became more important. During years of Richardson's ground squirrel abundance, weasels may temporarily switch predation onto these rodents.