Abstract： Objective To explore the radiosensitizatian of paclitaxel in human lung adenocareinoma cells. Methods A human lung adenocarcinoma cell line A973 was used in this study. The cytotoxicity of paclitaxel was investigated by using clonngenic assay to define the IC10,IC50 and IC90. The cells received either radiation(with different doses) alone or paclitaxel administrated before and after irradiation. Cell survival fractions were determined by clonogenic assay. Single hit multi-target model was used to determine survival curve parameters. Flow cytometry was performed to analyze the cell cycle distribution. Results The IC10, IC50 and IC90 of paclitaxel in A973 cells were 0.5,2.6 and 8.7 nmol/L,respectively. According to Do,Dq and SF2 value,the sensitivity enhancement ratio(SER) of IC10 was 0.97,1.01 and 2.00 when paclitaxel was added before irradiation, and 0.97,1.02 and 1.02 when after irradiation ; The SER of IC50 was 1.06,129.00 and 2.61 when paclitaxel was added before irradiation, and 0.94,220. O0 and 2.14 when after irradiation ;The SER of IC90 were 1.00,220. 00 and 2.09 when paclitaxel was added before irradiation,and 0.98,220.00 and 2.09 when after irradiation. The IC10 of paclitaxei failed to increase G2+M arrest of A973 cells.The maximal G2+M accumulation was reached at 2 h and 18 h after IC50 and IC90 of paclitaxel treatment,respectively. Conclusions Paclitaxel is able to enhance the radiation sensitivity of A973 cells. Sequence of treatment is not associated with radiosensitivity. Moderate and high dose of paclitaxel combined with low-dose radiation can produce the best effect of radiosensitiation.