We investigated the diet of the western terrestrial garter snake (Thamnophis elegans) along the Grande Ronde River in southeastern Washington. Snakes were collected with mass, snout-vent length and sex recorded. Of the 38 snakes collected 27 contained 31 prey items. The most abundant prey item was sculpin fish (Cottus spp.) (81.5%). There was no statistically significant relationship between size or sex of snake and prey presence, absence or size. Our data demonstrate that there is no change in prey base in relation to snake size or age. This is also the first population of Thamnophis elegans shown to specialize on Cottid fish in October, pre-overwintering hibernation.