BACKGROUND The cohesin loading factor, nipped-B-like protein (NIPBL), is also known as the sister chromatid cohesion 2 (SCC2) human homolog. Recently, we have studied the role of expression levels of NIPBL in cell proliferation and chemotherapy resistance of non-small cell lung cancer (NSCLC) cells in vitro. The aim of this study was to investigate the effects of expression of the cohesin loading factor, NIPBL, on the cell cycle, apoptosis, and autophagy of breast cancer cell lines in vitro. MATERIAL AND METHODS Expression levels of the NIPBL in the breast cancer cell lines, MCF7, Bcap37, MDA-MB 453 and MDA-MB 231, were measured using Western blot and flow cytometry. Small interfering RNA (si-RNA) was used to study the biological functions of NIPBL. The cell counting kit-8 (CCK-8) assay and the colony formation assay were used to measure cell proliferation; the wound scratching assay and transwell chamber assay were used to investigate cell invasion and migration. RESULTS NIPBL gene and protein expression were upregulated in the MCF7 and Bcap37 cells; si-NIPBL transfection inhibited cell proliferation, invasion, and migration of breast cancer cells. Downregulation of NIPBL arrested cells in the G0/G1 phase of the cell cycle and induced apoptosis and autophagy of breast cancer cells through the caspase3 and mammalian target of rapamycin (mTOR) signaling pathways. CONCLUSIONS [color=black]Downregulation of cohesin loading factor NIPBL arrested breast cancer cells in vitro in the G0/G1 phase of the cell cycle and induced apoptosis and autophagy. [/color].