We examined 15 species of ornamental tropical fishes originating from Southeast Asia to determine the cause of losses among 8 fish farms in Korea. A total of 351 individuals belonging to 5 different families (1 species of Characidae, 6 of Cichlidae, 3 of Cyprinidae, 1 of Heleostomatidae, and 4 of Poecilidae) were collected for the purpose of detecting metazoan and protozoan parasites. Parasites were fixed and stained using routine methods, and identified. We found 3 ciliates, 2 monogeneans, 1 nematode, and 1 copepod from 7 host species. Of these, Ichthyophthirius multifiliis was the most common parasite in our study, and together with Trichodina sp., caused mass mortality of Sumatra barb Puntius tetrazona at 1 farm. We also found Camallanus cotti and Tetrahymena corlissi from guppies Poecilia reticulata, both for the first time in Korea. Farmers consider these 2 pathogens to be the most serious ones in Korea. Gussevia asota from oscar Astronotus ocellatus, and Gyrodactylus bullatarudis from platy Xiphophorus maculatus were also found in Korea for the first time. We believe that appropriate quarantine practices for tropical ornamental fishes should be introduced because the failure to require and implement quarantines has already resulted in the accidental introduction of exotic parasites to fish farms, and because these parasites can cause further economic losses if they become established in the wild.