Resumo. The objective of this research was to collect, to study and to characterize the fauna of lepidopterous associated with Eucalyptus spp., plantation in the Municipality of Pinheiro Machado, in RS state. In the period of October 2005 to October 2007, every 15 days, collections of insects were accomplished with three light traps. After selection and transfixion procedures, the lepidopterous were identified based on entomological collections and specialized literature. Two thousand and twenty individuals belonging to 14 families, 106 genera and 220 species were collected. The families with the highest number of species collected were: Noctuidae (59), Geometridae (30), Arctiidae (28) and Saturniidae (14). According to the fauna classification the most species were considered not dominant, uncommon, rare and accidental. Among the species identified, there were some whose larvae are defoliators of the eucalypts: Oxydia agliata, (Geometridae), Sarsina violascens (Lymantriidae), Automeris illustris, Eacles imperialis magnifica and Lonomia obliqua (Saturniidae), which needs to have their populations monitored.