Abstract: Objective To identify and illuminate the effect and the mechanism of Caspase-3 gene of mediating X-radiation induced apoptosis in Nasopharyngeal carcinoma (NPC). Methods The CNE-2 cells were exposed in X-radiation with different doses and incubated for different hours. Apoptosis were measured using Electron Microscopy(ECM) for morphology and Flow Cytometry (FCM) analysis with Annexin -Ⅴ/PI dual staining for apoptotic cell ratio. The Caspase-3 mRNA and protein expression and enzyme activity in CNE-2 cells were investigated with RT-PCR, Western blot and colorimetric assay respectively. Results The predominant death model of NPC cells irradiated by X-radiation caused apoptosis, and the apoptotic ratio was at dose and time dependent patterns；the Caspase-3 enzyme activity was significantly increased in apoptotic cells. With AC-DEVD-CHO inhibiting the enzyme activity, the apoptotic ratio of CNE-2 cells was decrease markedly (P<0.05)and the character of apoptosis was not typical. The expression of Caspase-3 mRNA in apoptotic CNE-2 cells was not significantly increased. The expression of protein was17kd active-Caspase-3 in apoptotic CNE-2 cells, while the 32kD pro-Caspase-3 was dominant in control CNE-2 cells. Conclusion CNE-2 cells appeared characteristic apoptosis after X-radiation. The activity of Caspase-3 plays an important role in apoptosis. The elevation of Caspase-3 activity in CNE-2 cell may due to pro-caspase-3 being activated, not at transcription level.Apoptosis could be restrained or retarded after the activation of Caspase-3 being inhibited.