Objective To investigate the effect and probable mechanism of icaritin ( ICT) on EL-4 cells in vitro．Methods MTT、transmission electron microscope ( TEM)、flow cytometry analysis were used to examine the effect of ICT on the proliferation of EL-4 cells． Reverse transcript-polymerase chain reaction ( RT-PCR) assay and colorimetric method was used to reveal the probable mechanism． Results ICT could inhibit the proliferation of EL-4 cells significantly in a dose-and time-dependent manner． Apoptotic cells were observed by TEM and flow cytometry analysis． RT-PCR analysis showed that the expression of bcl-2、P21 were down-regulated． Besides ，Caspase-3 and Caspase-9 activity in EL-4 cells elevated remarkably． Conclusions ICT could inhibit the proliferation of EL-4 cells and induce EL-4 cells apoptosis in vitro． The probable mechanism may be down-regulate the expression of bcl-2、P21and elevate Caspase-3 and Caspase-9 activity in EL-4 cells．