Abstract: Objective 　To investigate the anti2tumor effect and explore it s mechanisms of celecoxib (a selec2 tive cox22 inhibitor) combined with 52fluorouracil (52Fu) on the t reatment of human colorectal cancer in BALB/ C nude mice subcutaneous xenograf t model. Methods 　Effect s of celecoxib combined 52Fu on the proliferatic in xenograf t carcinoma induced by HT229 were investigated. Simultaneously the method of im2 munohistochemist ry and western blot were used to estimate the expression of Cytochrome C、caspase23 and caspase29, the apoptosis morphous was detected by elect ron microscope and the apoptosis of tumor cell was detected by TUNEL to determine apoptotic index ( A I) . Results 　The effect of synergistic usage of 52Fu and celecoxib for the t reatment of human colorectal cancer was better than other groups. The re2 spective rates of the tumor inhibition of B group, C group and D group were 27. 81 %、53. 02 %、78. 37 %, and the differences compared with cont rol group (0) were significant ( P < 0. 01) . Compared with cont rol group the apoptosis of tumor cell in t reated groups notably raised and the statistical differences of the ap2 optotic index ( A I) among t reated group s were significant ( P < 0. 01) . The means of fimmunohistochemis2 t ry and western blot display that the expression of Cytochrome C、caspase23 and caspase29 of t reated groups increased obviously compared with the cont rol group . Meanwhile the statistical differences of the expression of Cytochrome C、caspase23 and caspase29 among the t reated groups were also significant ( P <0. 05) . Conclusion 　Celecoxib and 52Fu have respective effect to inhibit the growth of tumor. Compared with celecoxib or 52Fu individual drug group, Celecoxib combined with 52Fu significantly inhibited the growth of human colorectal cancer in nude mice subcutaneous xenograf t . The mechanism of antitumor maybe is correlate with inducing apoptosis and activation mitochondrion accommodation pathway by up2 regulating the expression of Cytochrome C、caspase23 and caspase29.