Residual cell DNA(RC DNA) in the products of recombinant human intederon γ(IFN-γ)was detected by hybridization with digoxigenin-labeled total DNA of E.coli DH5α-pBV220/IFN-γ as probes,The result showed a great disparity between two DNA standards in colour;thus indicating that high protein amount interfere seriously in the detection of trace RC DNA and that the DNA standard supplied with IFN-γ is more reasonable than the homogeneous one.The sensitivity of the method is 4 pg and RC DNA amount existed in each dose of all samples is less than 100 pg，which satisfied WHO requirements.