The experiment was conducted in order to determine the short term (96h) total ammonia tolerance level of four freshwater fish species to prevent their accidental mortality caused by ammonia toxicity. Fingerling (8±0.5g) of Catla catla, Labeo bata, Cyprinus carpio and Oreochromis mossambica were exposed to 5, 10, 15, 20, 25, 30 and 40mg/l concentration of total ammonia. Mortality of fishes was recorded at 12h interval in different treatments. Results obtained from the study revealed that 50% mortality of Catla catla, Labeo bata, Cyprinus carpio and Oreochromis mossambica was observed in 15, 10, 25 and 30mg/l respectively. It, therefore, can be concluded that LC50 were 15, 10, 25 and 30 mg/l in Catla catla, Labeo bata, Cyprinus carpio and Oreochromis mossambica, respectively and which also clearly indicated that total ammonia tolerance level was maximum in Oreochromis mossambica which followed by Cyprinus carpio Catla catla and Labeo bata. Because of the accumulation of ammonia was lower in tilapia and higher in bata due to different enzymatic activity in its metabolic conversion process.