The study of fauna through long-term surveys is important in unveiling how temporal patterns shape the structure of communities in tropical habitats. The butterfly assemblage of the subtropical Atlantic Forest may be considered highly diverse and shows changes in diversity and composition over time, highlighting the importance of long-term inventories. This work assessed temporal diversity patterns in the distribution and composition of butterfly assemblages in an Atlantic Forest site in southern Brazil using combined data from three years of standardized sampling with entomological nets, increasing the knowledge on this group in the Neotropics for monitoring and conservation. The butterfly fauna was analyzed in terms of richness, abundance, and composition. The inventories reached 401 species, with 14,442 butterfly individuals sampled. All the diversity parameters evaluated show significant differences between the first year of sampling compared to the second and third years. The latter had higher values of richness and abundance, followed by the first and second years. Hesperiidae was the richest family, followed by Nymphalidae and Lycaenidae, indicating a good representation of the assemblage as a whole. The results of this work are important for developing conservation programs in the Atlantic Forest and other forested environments in the neotropics, especially concerning reliable diversity assessments for the monitoring and management of protected areas. Decision making and public policy might also benefit from knowledge on temporal patterns of diversity regarding the maintenance of native habitats and integrity of biomes and their associated fauna.