Tomatoes belong to the Solanaceae (the nightshade family). Lycopersicon esculentum is a perennial plant in the tropics but in northern climates it is grown as an annual. Botanically this vegetable is a fruit (a berry). The tomato is a native of the Peru,Bolivia and Ecuador area of the Andes Mountains. It is found in great varieties and types,which are consumed worldwide, because of its highly nutritious values. Export of tomatoes from Pakistan is less because of post harvest losses. To reduce the post harvest losses,radiation was chosen as a treatment. The present study focused on the effect of Gamma radiation (cobalt-60) on tomatoes in order to check their effect on residing micro flora. For this purpose, micro flora of tomatoes was determined and different doses of radiation were given to tomatoes. The best dose optimizes was 1 kGy that not only reduces the micro flora but also increases the shelf life of tomatoes for a period of 21 days.