Vitamin A and its derivatives (known as retinoids) play a crucial role in vision, inhibition of cell proliferation, cell division and differentiation and Fetal development. The active form of vitamin A is retinol, also known as vitamin A1 is found in animal products as preformed vitamin A. All-trans-retinol (vitamin A) has been studied as antioxidant in in vitro but limited data is available on cytotoxic effects of retinol on cancer cell lines. In this paper, the cytotoxic effects of retinol on breast cancer cells (MDA-MB-231) and prostate cancer cells (PC-3) were studied. Our experiments showed that maximum cytotoxicity was achieved at 48 hours and at 100µM concentration of all-trans-retinol on both the cell lines. The results have significant implications for understanding anti-cancer effects of all-trans-retinol on breast and prostate cancer cell lines.