Murine lymphoid leukemia L,7712, cells were incubated with various concentrations of PSD-007, the inhibition of DNA synthesis was observed, the degree of inhibition was proportional to the concentration of the PSD-007 (below 10 µg/ml) in the cultural medium, the inhibition increased slowly above that level.,There were no differences in the degree of DNA strand breaks between 10 Gy γ-ray irradiated cells versus PSD-007 treated cells irradiated at the same dose in dark. It showed PSD-007 was unable to induce the effect of ionizing radiation on DNA damage in dark. However, when the treated cells alone were irradiated by 10 Gy γ-ray in visible light, the degree of DNA strand breaks increased distinctly and gave a clear difference versus protected from light group respectively, whereas the treated cells alone exposed to visible light at same conditions, there could not be observed any DNA damage. These results showed that PSD-007 could sole enhance the DNA strand breaks of L,7712, cells by ,γ, ray irradiation under visible light. This new phenomenon denoted that PSD also may be used in cancer radiotherapy under some circumstances.,The effects of PSD-007 and/or ,γ, ray radiation on DNA and the influence of many factors on assay methods are discussed.