Beef longissimus dorsi steaks were treated with 10, 25, and 50-kGy gamma irradiation and weekly examined during refrigeration storage at 5ºC to evaluate the changes in their organoleptic, bacteriological, chemical and nutritional quality characteristics as well as deterioration criteria. The signs of spoilage became apparent after 17 days of refrigeration storage in control untreated samples compared with 52 days for 10 kGy treated samples; however, samples treated with 25 or 50 kGy remained without signs of spoilage until the end of storage period (4 months). A characteristic burnt flavor was distinguished in irradiated beef samples, which was intensified with high irradiation dose, but decreased during storage. High doses of irradiation especially 50 kGy resulted in a brownish color of meat surface. Moreover, gamma irradiation resulted in high thiobarbituric acid values after treatments and during storage due to lipid oxidation. Thiamin content of beef was severely reduced and the reduction was dependant on the irradiation dose. Riboflavin was also affected by irradiation, but it was much stable than thiamin. The proximate chemical composition of beef was slightly affected by irradiation.