The Can Gio Mangrove Biosphere Reserve is a unique transitional ecosystem between land and sea and represents a significant wetland area in southern Vietnam. Despite being recognized as a biodiversity hotspot, its butterfly fauna remains poorly documented. In this study, the Pollard Walk method was using on 72 sampling events in 12 fixed transects to we present the first comprehensive checklist and diversity assessment of butterflies (Lepidoptera: Rhopalocera) from this region. A total of 46 species, belonging to 37 genera and 5 families, were recorded through systematic field surveys conducted across 12 sites during both dry and rainy seasons from 2024 to 2025. The family Nymphalidae exhibited the highest species richness (19 species), followed by Lycaenidae (9 species), Pieridae (7 species), and Hesperiidae (7 species). Two species of most abundance were identified: Catopsilia pomona and Ixias pyrene. Our findings reveal that the butterfly community in Can Gio is moderately diverse (H’ = 1.66 ± 0.52) and exhibits seasonal variation in species composition and abundance. The study provides baseline data for future biodiversity monitoring and highlights the importance of preserving the mosaic of habitats within this mangrove biosphere reserve.