Objective To study the effect of E1A gene on the radiosensitivity of nasopharyngeal carcinoma (NPC) cells and its mechanism. Methods Ad-E1A gene was transfected into human NPC cells (CNE2), then the positive clones (CNE2-Ad-E1A) were identified by RT-PCR. CNE2 cells, CNE2 cells transfected with Ad-β-gal (CNE2-Ad-β-gal) and CNE2-Ad-E1A cells were irradiated with 0 Gy,2 Gy,4 Gy,6 Gy and 8 Gy respectively using 6 MV X-ray. Clone forming assays were carried out, cell survival curves were drawn and the sensitivity enhancing ratio (SER) was calculated. The redistributions of cell cy-cle were analyzed by flow cytometry. RT-PCR was used to detect the expression of wtp53. Results RT-PCR confirmed that E1A gene had been integTated into positively transfected cells and stably expressed. Cell survival curves showed that the SER of D0,Dq and SF_2 value was 1.37, 1.95 and 1.46 in CNE2-Ad-E1A cells. The D_0,D_q and SF_2 value was 1.57 Gy,1.82 Gy, 0.89 in CNE-2 cells and 1.53 Gy,1.78 Gy,0.82 in CNE2-Ad-β-gal cells, respectively. The G_2/M arrest was shown in CNE2-Ad-E1A cells. Moreover, the expression of wtp53 gene was markedly enhanced in Ad-E1A-CNE2 cells. Conclusions E1A gene can ef-fectively enhance the radiosensitivity of human NPC cells, which may be associated the enhancement of wt-p53 expression and G_2/M arrest.