Although secondary forests comprise half of the world’s remaining tropical forests, their role in biodiversity conservation remains poorly known. This study aimed to evaluate the role of secondary forests in conserving dung beetle biodiversity in karst ecosystems of Vietnam. In total, 60 baited-pitfall traps were deployed to investigate dung-beetle communities in the old secondary forests (>40 years) and primary forests across two study areas: Pia Oac National Park (Cao Bang Province) and Pu Luong Nature Reserve (Thanh Hoa Province). In total, 38 dung-beetle species of 1,266 individuals were sampled and identified from the trapping sites in the two study areas. The generalizsed linear models (GLMs) showed no significant difference in species richness, abundance and biomass of dung beetles between the old secondary forests and the primary forests, and this result was consistent throughout both the study areas. This finding seemed to give hope for the recovery of dung beetle communities during forest succession. In contrast, the community structure still differed significantly between the primary forests and the old secondary forests according to the permutational multivariate analysis of variance (PERMANOVA) (Pia Oac: F=8.92, p<0,001; Pu Luong: F=6.78, p<0,001). Particularly, a decline in the number of large-bodied tunnellers in the old secondary forests might negatively affect the dung removal rate of the dung beetle communities, being an important ecosystem function in tropical forests.