Development of a combination of gamma irradiation and trisodium phosphate (TSP) for preservation of fish fillets and improvement of its microbiological quality were studied. Irradiation doses of 1, 2 and 3 KGy were applied to the first group of the prepared samples; dipping in 1.5, 3 and 5% TSP concentrations was applied to the second group of samples, then a combination of irradiation and TSP treatments have been applied to the third group of the prepared samples. The results revealed that irradiation alone was effective in eliminating most of the detected organisms of importance in fish fillets gradually as the dose of irradiation increased. Immersion of fish fillets in TSP alone was not enough to reduce the microbial population while combination of 3% TSP and 1 kGy of irradiation resulted in great reduction in the counts of the contaminating microorganisms. However combination of 3% TSP and 2 kGy of irradiation reduced the aerobic plate count to less than 2 log cycles with the best sensory and chemical attributes