Most breast cancers originate in the lobules or ducts of the breast. Breast cancer as the second main cause of death among women in the world is the most common kind of cancer in women. Studies have been conducted to find the optimal treatment for breast cancer. Moreover, the therapeutic effects of different drugs and substances on this disease have been intensively researched. Boric acid accounts for 96% of the boron content in body fluids, and its derivatives are absorbed by the human body. It is assumed to be represented as (B(OH)2). Experimental studies have shown a reduction of cell proliferation and stimulation of apoptosis in some melanoma, prostate, and colon cancer cell lines through boric acid. The aim of this study was to investigate if boric acid could be used for treating breast cancer. The impacts of boric acid on the human breast carcinoma cell lines MCF-7 and MDA-MB-231 were studied with TUNEL, BrdU, caspase-3, and endo-G immunohistochemical studies in 3D and 2D culture systems. Furthermore, we conducted a qRT-PCR study to show changes in the expression of some genes involved in apoptosis. Suppression of cell proliferation through boric acid–inducing apoptosis was observed both in 3D and 2D culture conditions. These results are compatible with the gene expression results. The ENDOG, CASP3, CASP8, and CASP9 gene expression significantly changed at all time intervals in MCF-7 and MD-MB-231 cell lines boric acid can potentially treat breast cancer as an anti-cancer agent candidate.