Abstract: Objective To investigate the effects of histone deacetylase inhibitor（HDACi）, chidamide, on proliferation， apoptosis and infiltration in triple negative breast cancer CAL51 cell line in vitro. Methods The real time cellular analysis （RTCA） assay was employed to detect proliferation inhibition efficiency by treating cells with different concentration groups of chidamide （0， 5， 10， 20， 50， 100μmol／L）. When CAL-51 cells were treated with chidamide （10， 15， 20μmol／L） for 72h， morphological changes of CAL-51 were observed under inverse microscopy. The cell apoptosis， cell cycles and stem cell proportion were analyzed by flow cytometry. RTCA assay was used to detect changes of infiltration ability after treatment. Results Chidamide was able to inhibit proliferation of CAL51 cells in vitro in a positive concentration dependent manner （r=0.791，P＜0.001）. After being treated with chidamide， cell morphology appeared great changes. Flow cytometry assay showed obvious apoptosis compared with control group with the increase of drug concentration and acting hours （P＜0.05）， but no alternation of cell cycles and stem cell proportion were detected. RTCA assay showed that cell infiltration ability was obviously inhibited after treatment. With the increase of drug concentration， the inhibition of cell invasion ability increased significantly （P＜0.05）. Conclusion Chidamide can obviously inhibit the proliferation of CAL-51 cells， induce its apoptosis and reduce the cell invasion and infiltration capacity.