A snake richness of 56 species was recorded at Espigão do Oeste (Rondônia), with a faunal composition very similar to that of the closely located area of the Hydroelectric Power Plant of Samuel (Rondônia). The most abundant species were Liophis reginae (18.6% of the total), Oxyrhopus melanogenys (8.4%), Chironius exoletus (6%), Boa constrictor (5.8%), Dipsas catesbyi (5.6%), and Drymarchon corais (5.6%). A smaller number of snakes was recorded during the driest months (from June to August). Most species feed on lizards (55.3% of the species), followed by anurans (48.2%), mammals (26.8%), birds (12.5%), and snakes (12.5%). A cluster analysis was carried out to produce a dendrogram with information on size (snout-vent length), feeding habits, activity time, and foraging substratum. Eight guilds of snakes were found, according to similarities in resources use. The cluster analysis grouped together both closely or distantly related species, showing that both historical and ecological factors were important in structuring the assemblage.