Abstract: Objective 　To explore the correlation between DNA-ploidy and radiosensitivity and prognosis of nasopharyngeal carcinoma ( NPC ) . Methods 　The DNA-ploidy of 45 cases NPC cells was analyzed before the radiotherapy by means of FCM. The short-term curative effect was assessed in the sixth month after the radiotherapy was end up . The patient s were followed up periodically af ter the t reatment . And the relationship between DNA-ploidy and radiosensitivity and prognosis was then statistically analyzed . Results 　There was no relationship between DNA-ploidy and the sex and pathologic type. But there was a remarkable correlation between DNA-ploidy and the following factors : clinical stage, short-term curative effect, radiosensitivity and prognosis. The percentage of the DNA aneuploidy in early stage ( Ⅰ+ Ⅱstage) was 11. 11 %(2/ 18), while in late stage ( Ⅲ+ Ⅳstage) it was 40. 74 %(11/ 27) ( P < 0. 05) . The aneuploidy tumors were more radiosensitive than the diploidy tumors ( P < 0. 01) and the short-term curative effect of the aneuploidy tumors was much better than that of the diploidy tumors ( P < 0. 05) . But the prognosis of the aneuploidy tumors were much more poor than that of the diploidy tumors ( P < 0. 01) . Conclusion 　Based on these findings, DNA-ploidy is considered as an independent factor of radiosensitivity and prognosis for NPC. The analysis of DNA-ploidy by means of FCM may be as an objective index to choose different divide-up radiotherapy for each individual patient of NPC.