Fish passage facilities are constructed to enable fish to pass anthropogenic barriers such as dams though their efficiency varies across species and location. There are a number of studies that assess the efficiency of fish passage facilities, yet rarely have such assessments been conducted in Asia. We conducted one of the first quantitative assessments of the efficiency of a vertical-slot fishway in Asia on the Daduhe River in Southwest China. Quantitative assessment of fish passage efficiency was conducted using a combination of methods, including fish sampling, video recordings and a Passive Integrated Transponder (PIT) system for tracking individually-tagged fish (N = 69 of 6 species). Fish sampling revealed 40 species assembled downstream of the dam. Fish captured closer to the fishway tended to be larger than fish caught more distant from the fishway. Half of the fish species observed downstream of the fishway were also observed at the entrance to the fishway (i.e. 153 individuals across 20 species). Video records revealed that overall passage rates were 71.2% based on the number of fish observed at the exit of the viewing chamber relative to that observed passing the entrance viewing chamber. Most fish passed the fishway at night with peak passage occurring in June. PIT technology results revealed that passage efficiency among the six tagged species ranged from 0% to 60% (four species successfully ascended the fishway). Transit time from the fishway entrance to exit was variable both among and within species that successfully ascended the fishway (i.e. 17.9-20.3 h for Schizothorax davidi, 6.4-88.8 h for Schizothorax preuanti, 46.4 h for Silurus meridionalis, 22.1-53.9 h Semilabeo prochilus). Fishway performance varied by species such that there is evidence that the fishway may be useful for maintaining river connectivity for some species. However, passage was often restricted during periods when there was sufficient flow in the fishway. Additional research is needed to put these findings in an ecological context given the overall low number of fish that passed the dam.