The objectives of this study are two folded: (1) to record fish composition, and (2) to assess the conservation potentials for native fishes in the urban ponds of southern Taiwan. We selected 18 urban ponds in Kaohsiung and Pingtung areas as the sampling sites. Sampling work lasted from October 2019 to March 2020, and four landscape features and 16 environmental variables were measured. Fish sampling was conducted by 10 cast nets per pond, and oral surveys and harvest checking with anglers were performed, ensuring our collections covered the majority of fish composition in each pond. With the exception of one pond where no fish was collected, 20 fish species, including 15 exotic species and five native ones, were recorded from 1,189 individuals in 17 ponds. Both common and near-threatened native species were found, indicating that the urban ponds were able to conserve and support the populations of native and threatened fishes. The first five years after establishing the urban ponds are the critical period for native fishes to be sustained based on a negative correlation between the established ages of ponds and number of native fishes. By integrating a negative correlation between existence ages of ponds and number of native fishes as well as both positive correlations between NO3-N concentration with total fish species and exotic fish species, we hypothesize that increasing nutrient concentration as the pond aged, possibly the consequence of domestic sewage and excretion of exotic fishes, may enhance the surviving prospects of exotic fishes in the urban ponds of southern Taiwan.