Monoamine oxidase (MAO) inhibitors have been tested for the purpose of treating many types of cancers including breast cancer. Pargyline, an MAO inhibitor, prevents the activity of lysine-specific demethylase 1 (LSD1), which is excessively expressed in breast cancer. The purpose of this study is to investigate the effect of pargyline on cellular proliferation in human breast ductal carcinoma (T47D) cells. After exposing T47D cells to pargyline, we examined cell proliferation, cell cycle, apoptosis, and the expression levels of apoptosis-related proteins and LSD1. The proliferation of cells exposed to pargyline decreased in a dose- and time-dependent manner. The treatment of 2 mM pargyline exhibited an increase of the cell proportion at the G1 phase, while the major decrease of the cell proportion was at the S phase compared to the controls. In addition, pargyline induced an increase in the cleaved PARP expression. However, we did not find a change in the LSD1 expression in the cells exposed to pargyline. Based on our results, it is believed that pargyline has pharmaceutical potential as an anticancer drug for the treatment of human breast cancer.