We present natural history details of 53 species, comprising six families (Aniliidae, Boidae, Colubridae, Dipsadidae, Elapidae and Viperidae), from “Floresta Nacional de Caxiuanã” and surrounding areas. Active species were reported during the day and night. We found exclusively terrestrial snakes (e.g. Drymoluber dichrous, Mastigodryas boddaerti and Dendrophidion dendrophis), species that forage ... [Show full abstract] on the ground and on the vegetation (e.g. Chironius fuscus and Philodryas viridissima), and exclusively arboreal snakes (Corallus hortulanus, C. batesii, among others). Most snakes feed on lizards and/or anurans. We identified 11 potentially specialist species: Atractus schach and A. major (worms); Dipsas catesbyi (molluscs - snails); Helicops polylepis, H. trivittatus, Hydrops martii and H. triangularis (fish); Siphlophis cervinus (lizards); Dendrophidion dendrophis and Xenopholis scalaris (anurans); and Tantilla melanocephala (centipedes). The specimens tend to have a continuous reproductive cycle. Females were reported with eggs/embryos, recent nesting marks and offspring throughout the year. We reported several defensive behaviors, among which, prey regurgitation, dorsoventral flattening of the body, tail lifting, S-coil, cloacal discharge, biting, protecting the head under the body, and escaping. Besides, some snakes mimic coral snakes (e.g. Erythrolamprus aesculapii and Anilius scytale) and pit vipers (e.g. Xenodon rabdocephalus).