With the health concerns of menopausal hormone replacement therapy, alternatives have been sought. Klimaktoplan® is a homeopathic formulation consisting of four main components and has been used for relief of menopausal symptoms for a long time. The study investigated the safety of Klimaktoplan® through its effect on the proliferation of breast cancer (MCF-7) and non-malignant mammary epithelial cells (MCF-10A). MCF-7 and MCF-10A cells were cultured in 312.5, 625, and 1,250 μg/ml Klimaktoplan®. 17-Beta estradiol (E2) and medroxyprogesterone 17-acetate (MPA) were used for comparison with Klimaktoplan®. E2 only (0.001, 0.01, and 0.1 μM), and the combination of E2 (0.001, 0.01, and 0.1 μM) and MPA (0.01, 0.1, and 1 μM) were tested. Control cells for Klimaktoplan® and E2 groups were treated with dimethylsulfoxide (DMSO), and DMSO + ethanol was used for the combination group. Cellular proliferation was evaluated by the formation of insoluble formazan after incubation of 4 days. Klimaktoplan® had a concentration-dependent anti-proliferative effect on breast cancer cells at 625 and 1,250 μg/ml, while not affecting proliferation of non-malignant mammary cells at any tested concentration. The effect of lactose was evaluated as lactose (the adjuvant of Klimaktoplan®) affect cell growth. E2 and lactose increased the proliferation of both malignant and non-malignant cells. The effect of E2 + MPA on the proliferation of malignant and non-malignant mammary cells was lower than estradiol only, but was higher than control. Klimaktoplan® has an anti-proliferative effect on breast cancer cells, but not for non-malignant mammary epithelial cells, unlike E2 and E2 + P. With further research, KP would be a good alternative or additive in women with menopausal symptoms who wish to avoid conventional E or E + P hormone therapy.