Abstract: Objective 　To investigate the growth effects of the selective cyclooxygenase-2 inhibitor Nimesulide on human bladder cancer cell line T24 in vitro, and to clarify its probable mechanism. Methods 　 The T24 cell line was culture in vitro, and exposed to a range of concent rations of Nimesulide at different time. The effect of COX-2 inhibitor Nimesulide on the proliferation and apoptosis of human bladder cancer cell line T24 in vit ro were observed by using cell morphology, MTT assay, flow cytomet ry, fluorescent microscopy. Results 　Significant cytotoxicity of cyclooxygenase-2 inhibitor Nimesulide on human bladder cancer cell line T24 were observed by cell morphology. MTT assay and flow cytometry show that cyclooxygenase-2 inhibitor Nimesulide significantly inhibited cell proliferation of T24 cell line in vit ro in a dose-and time-dependent manner . Cell-cycle analysis by flow cytometry suggested that Nimesulide induced a decrease in S and G₂ / M phase population and a significant increase in G₀ / G₁ population compared with unt reated T24 cells. And a typical subdiploid peak before Phase G₀ / G₁ was detected by flow cytometry. The rates of apoptosis were correlated with the concent ration of Nimesulide and time of action. A typical apoptosis morphology were also observed by fluorescent microscopy. Conclusion 　The selective cyclooxygenase-2 inhibitor Nimesulide has significant inhibit effects on the growth of T24 cell, which is closely related to block cell cycle and apoptosis-inducing.