This study was performed to investigate antimicrobial, antioxidant, and anticancer properties of Opuntia humifusa (OH) stems. OH stems were extracted with hexane, methanol, butanol and water. The methanol and hexane fraction exhibited strong antimicrobial activities on three strains of microbes, Rhodococcus equi, Staphylococcus aureus, and Clostridium perfringens. In the peroxynitrite scavenging effect (ONOO-) of OH stems, the antioxidative activity of methanol, butanol and water fraction but not hexane fraction showed significant increases in a concentration-dependent manner. The DPPH radical scavenging activities of OH stems were high in the butanol fraction compared with other fractions. Anti-proliferation effects on the B16-F10, HepG2, HT29, and MCF-7 cell lines were significantly higher in the methanol and hexane fractions than in the water and butanol fractions at 100 μg/mL concentration of extracts. These results suggest that OH stems can be used for the development of functional foods with biological activity.