Genetic Variation of Keprok SoE Mandarin (Citrus reticulata Blanco) Resulted from Gamma Iradiation Based on ISSR Markers. SoE mandarin is one of the best mandarin from Indonesia which has been chosen as one of mandarin for import substitution. The citrus quality could be improved through breeding program, one of this program was mutation breeding using gamma rays irradiation. The research was aimed to obtain information of SoE mandarin genetic variation derived from gamma rays irradiation using ISSR marker. The research was conducted at Breeding and Tissue Culture Laboratory of Indonesian Citrus and Subtropical Research Institute (ICISFRI) from May to September 2008. Five ISSR primers were used to amplify DNA samples. Matrix data was counted and dendrogram of samples was established using UPGMA and SAHN methods. The resulst showed that 3 of the primers indicated polymorphism. About 22 locus were amplified from 3 primers, 9 (40.9%) locus showed polymorphism. The genetic similarity of SoE mandarin derived from gamma rays irradiation were 73-100%.