Objective: To evaluate the effect of the treatment by vinovelbine (NVB) and cisplatin (DDP) with radiation at dif- ferent timing intervals on the radiosensitivity of human breast cancer cell MCF-7. Methods: Six groups (at the interval of 0 h, 4 h, 12 h, 36 h, 48 h, 72 h between chemotherapy and radiotherapy) were studied by cologenic formation assay. In addition, the effect of different timing intervals between chemotherapy and radiotherapy on cell cycle distribution and apoptosis induc- tion in MCF-7 cells was also studied. Quantitation of the apopotic cells was performed by Flow cytometry measurements. For the qualitative detection, fluorescence microscopy analysis was used. Results: The six groups had different SF data, it was the lowest one at the intervals 12 h group, the middest one at 0 h groups, and the highest one at 48 h, 72 h groups when the radiation dose was 8 Gy. In some degree, the different SF data of the six groups could been explained by the different percent- age accumulation of G2/M phase at different timing caused by the NP chemotherapy. Apoptosis index after chemotherapy increased with time extending, but the changes of apoptosis index seem not correlate with the SF differences. Conclusion: The different timing intervals between NP chemotherapy and radiotherapy affect the radiosensitivity of MCF-7 cells, but those changes according to the interactive of cycle distribution and apoptosis. Objective: To evaluate the effect of the treatment by vinovelbine (NVB) and cisplatin (DDP) with radiation at dif- ferent timing intervals on the radiosensitivity of human breast cancer cell MCF-7. Methods: Six groups (at the interval of 0 h , 4 h, 12 h, 36 h, 48 h, 72 h between chemotherapy and radiotherapy) were studied by cologenic formation assay. In addition, the effect of different timing intervals between chemotherapy and radiotherapy on cell cycle distribution and apoptosis induc- tion in Quantitation of the apopotic cells was performed by Flow cytometry measurements. For the qualitative detection, fluorescence microscopy analysis was used. Results: The six groups had different SF data, it was the lowest one at the intervals 12 h group, the middest one at 0 h groups, and the highest one at 48 h, 72 h groups when the radiation dose was 8 Gy. In some degree, the different SF data of the six groups could been explained by the different percent- age acc umulation of G2 / M phase at different timing caused by the NP chemotherapy. Apoptosis index after chemotherapy increased with time extending, but the changes of apoptosis index seem not correlate with the SF differences. Conclusion: The different timing intervals between NP chemotherapy and radiotherapy affect the radiosensitivity of MCF-7 cells, but those changes according to the interactive of cycle distribution and apoptosis.