Objective:To study the effect of X-ray on expression levels of X-ray repair cross-complementing gene2(XRCC2)and XRCC3 in lung cancer cells,and explore the effect of DNA homologous recombination repair mechanism in radiotherapy of lung cancer. Methods:Cell inhibition ratio was measured using MTT assay. The expression levels of XRCC2 mRNA and XRCC3 mRNA in lung cancer cell line A549 were measured by RFQ-PCR assay. Results:The rate of proliferation inhibiting of lung cancer cells increased in line with the prolong radiation time of X-ray(P < 0.05)and the increase of radiation dose(P < 0.05),but there was no difference between the groups of 16 Gy and 32 Gy(P=0.211). The expression levels of XRCC2 and XRCC3 mRNA in these lung cancer cells increased significantly after treated with X-ray,and then decreased. The expression levels of XRCC2 and XRCC3 mRNA peaked at 48 h after X-ray treatment(P < 0.05). The expression levels of XRCC2 and XRCC3 mRNA increased markedly with the increase of radiation dose(P < 0.05). Conclusion:X-ray has a fairly obvious function to decrease proliferation of lung cancer cell,and could increase the expression levels of XRCC2 and XRCC3 mRNA in lung cancer cells. The results indicate that DNA homologous recombination repair mechanism may play an important role in resistance to radiotherapy in lung cancer cell.