Abstract: Post-harvest management of onions and potatoes is a sever problem in Iran. In this regard a research project of radiation preservation of root crops was carried out. Ten tones of red variety of onions and pashandi variety of potatoes were used every year of the trial. Bulbs were irradiated at a dose of 0.10 kGy and stored along with the unirradiated controls, at low temperature and under ambient conditions for a period of more than 7 months. After 4 months of storage under ambient conditions, the rotting ranged from 1 to 15% in irradiated onions and 5 to 64% in unirradiated samples. The unirradiated potatoes were discarded after 6 months of storage, because of heavy sprouting and rotting. It was found that losses through dehydration were 9.4 to 14.9% in the irradiated potatoes. Also a comparative study of reducing and non-reducing sugars, vitamin-C contents, total sugar, starch and protein was carried out between control and irradiated samples. The percentage weight loss varied between 25 to 36% after 6 months of storage in the irradiated onions and 18 to 29% for untreated samples.