Abstract: Objective 　To study the inhibitory effect of IFN-α1b on Endomet rial adenocarcinoma cell line JEC and it s mechanism by measuring the change of cell cycle and detecting the expression of p21, cyclin A and cyclin E. Methods 　Aftert reated by IFN-α1b at different concent rations 24 hours, the amount of cell was measured by cell count to learn the effect of IFN-α1b on the proliferation of JEC cell ; cell cycle phase and expression of p21, cyclin A and cyclin E were analyzed by flow cytomet ry ( FCM) . Results 　IFN2α1b all have inhibitory effect s at different concert rations, the st rongest of which is 500U/ ml. FCM shows that cells are accumulated in Sphase in cell cycle ; the expression of p21 and cyclin E increase but cyclin A reduces. Conclusion 　IFN-α1b can inhibit proliferation of the JEC cell and its mechanism relates to cell arrest in Sphase which is probably caused by the increased expression of p21 and the reduced expression of cyclin A.