we analyzed the survival rate through the measurement of germinability of the gamma-ray irradiated buds of 4 Citrus species, C. hybrid ‘Kiomi’, C. hybrid ‘Setoka’, C. hybrid ‘Kanpei’, and C. junos, in greenhouse. To induce mutation, spring buds of Citrus with 0, 10, 20, 40, 60, 80 and 100 Gy of gamma radiation were irradiated and then were vgrafted onto trifoliate orange rootstock. The rootstock number per gamma ray dosage was two hundreds. After after 6 months growth, the shoot germination rate from gamma ray-irradiated buds presented lower viability than those of non-irradiated buds. Higher dossage of irradiation more inhibited bud germination at all experimental groups of citrus. The viability of unirradiated citrus plants was C. junos > ‘Setoka’ > ‘Kiomi’ > ‘Kanpei’. We have determined LD50 of gamma ray-irradiation. This research was supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2010-0007627 and 2009-0094059), and by Golden Seed Project, Ministry of Agriculture, Food and Rural Affairs (MAFRA), Ministry of Oceans and Fisheries (MOF), Rural Development Administration (RDA) and Korea Forest Service (KFS), Republic of Korea