A total of 360 arbitrary 10-mer oligonucleotide primers were screened using RAPD (random amplified polymorphic DNA) technique on the genome DNA of Norin 8 and its ⁶⁰Co gamma-ray irradiation mutant Norin 8m. One primer OPG18 produced co-dominant polymorphic markers OPG18/972 and OPG18/943 from Norin 8 and Norin 8m. Based on the clones and sequences of the OPG18/972 and OPG18/943, it shows that a 29 bp DNA fragment in the genome DNA of Norin 8m is deleted. The results directly confirmed the fact that ⁶⁰Co gamma-ray irradiation can induced a bigger DNA fragment deletion of plant genome DNA.