Abstract: In order to get the best radiation dose of the 60Coγ-ray for variation induction in Phalaenopsis aphrodite cv. V31, the potted clonal plants were treated by different doses of 60Coγ-ray. The genomic DNA of treated and controlled plants was extracted from young leaf and amplified by using of RAPD-PCR technique. The 60 bands were amplified by using the 13 primers screened out from 40 ones and 26 bands of that were special. The cluster analysis of the bands amplified in treated and controlled plants showed that the variation degree was maximum in plants treated with 15Gy and was minimum in plants treated with 1Gy. Therefore 15Gy was the best radiation dose of the 60Coγ-ray for variation induction.