Abstract: To promote the reasonable application of genetically modified(GM)soybean, the effect of irradiation on the degradation of roundup ready soybean DNA was investigated.In this research, the roundup ready(RR)soybean and soybean flour were irradiated by Co⁶⁰ γ-ray at the dosage of 0, 4, and 10 kGy, resepectively.The mass concentration and molecular weight of the DNA as well as the copy number of the exogenous gene cp4 epsps of the irradiated sample were measured.The results showed that with the increase of irradiation dosage, the integrity of genome DNA in RR soybean and soybean flour tended to decrease, of which soybean flour decreased more.The copy number of the cp4 epsps gene declined as the dosage of irradiation raised.However, the amplications of long fragment lectin and cp4 epsps genes were still positive when the irradiation dosage increased to 10 kGy.Therefore, as a commonly used method for food treatment, irradiation could degrade DNA in RR soybean.The degradation degree of DNA in RR soybean flour was higher than that in intact soybean.Other treatments are still required to degrade RR soybean exogenous genes to a great extent.