Onion (Allium cepa L.) is one of the most widely grown vegetable in Pakistan and a means to earn valuable foreign exchange for the country. Microbial spoilage of onion is a major cause resulting in post harvest loss every year. In the present study, gamma radiation treatment was used to reduce the pathogenic microflora of Allium cepa L. hence increasing post harvest storage life. The major exported onion variety of Punjab (Desi Red) was selected for the study. The onion bulbs were irradiated at the doses of 0.05, 0.10 and 0.15 kGy at PARAS Foods, Lahore. Then the comparison of microbial populations of onion was made between control and irradiated samples. The impact of radiation dose on weight loss and organoleptic qualities of onion was also evaluated. The results revealed that gamma irradiation significantly affected bioburden, weight loss and organoleptic properties. Onion bulbs irradiated at the dose of 0.15 kGy showed minimum weight loss, reduced microbial load and preservation of organoleptic qualities of onions.