Breast cancer is the most frequent and lethal neoplastic disease among women worldwide. Psidium Guajava is a promising functional food against cancer, owing to a variety of bioactive compounds. This study aimed to evaluate the anticarcinogenic potential of Pedro Sato (PS), Hitigio (HI) and Tsumori (TS) guava cultivars fruit pulp extracts in MDA-MB-435 and MCF-7 human breast cancer cells. The antioxidant capacity of the extracts and their effect on cell viability, cell cycle and apoptosis were assessed. Additionally, the concentration of carotenoids, total phenolics, ascorbic acid and other physicochemical parameters were evaluated. PS pulp extract showed the highest in vitro antioxidative activity by all tested methods, as well as the highest content of lycopene and total phenolics, while TS pulp extract presented the highest concentration of β-carotene. After 48 hours treatment, all guava cultivars' extracts caused reduction of MDA-MB-435 and MCF-7 cells viability, with PS and HI being the most effective extracts. All guava extracts caused MDA-MB-435 and MCF-7 cell count reduction in G0/G1 and G2/M phases and increased apoptosis. The present results strongly suggest that guava pulp exerts antiproliferative effect on breast adenocarcinoma cells.