AIM:To investigate the effect of paeonol on controlling the proliferation of colorectal cancer cell line HT-29 and to discuss its possible mechanism. METHODS:The inhibitory effect of paeonol on proliferation of HT-29 cells was detected by MTT assay.The results of apoptosis were measured by flow cytometry.Immunocytochemical staining was performed to detect the expression of cyclooxygenase-2(COX-2)and protein p27 in HT-29 cells treated with paeonol at different concentrations. Reverse transcription-polymerase chain reaction(RTPCR)was used for mRNA analysis. RESULTS:From the data of both MTT and flow cytometry,we observed that cell proliferation was inhibited by different concentrations of paeonol.By immunocytochemical staining,we found that HT-29 cells treated with paeonol(0.024-1.504 mmol/L)reflected reduced expression of COX-2 and increased expression of p27 in a dose-dependent manner.RT-PCR showed that paeonol down-regulated COX-2 and up-regulated p27 in a dose-and time-dependent manner in HT-29 cells. CONCLUSION:One of the apoptotic mechanisms of paeonol is down-regulation of COX-2.p27 is upregulated simultaneously and plays an important part in controlling cell proliferation and is a crucial factor in the Fas/FasL apoptosis pathway. METHODS: The inhibitory effect of paeonol on proliferation of HT-29 cells was detected by MTT assay. The results of apoptosis were measured by flow cytometry. Immunocytochemical staining was performed to detect the expression of cyclooxygenase-2 (COX-2) and protein p27 in HT-29 cells treated with paeonol at different concentrations. Reverse transcription-polymerase chain reaction (RTPCR) was used for mRNA analysis. RESULTS: From the data of both MTT and flow cytometry, we observed that cell proliferation was inhibited by different concentrations of paeonol.By immunocytochemical staining, we found that HT-29 cells treated with paeonol (0.024-1.504 mmol / L ) reflected reduced expression of COX-2 and increased expression of p27 in a dose-dependent manner. RT-PCR showed that paeonol down-regulated COX-2 and up-regulated p27 in a dose-and time-dependent mann er in HT-29 cells. CONCLUSION: One of the apoptotic mechanisms of paeonol is down-regulation of COX-2.p27 is upregulated simultaneously and plays an important part in controlling cell proliferation and is a crucial factor in the Fas / FasL apoptosis pathway .