Magnesium oxide nanowires (MgONWs) were prepared using leaves extract of Prosopis farcta (P. farcta). Transmission electron microscope, atomic force microscope, X-ray diffraction, and fourier transform infrared spectroscopy were used to study the properties of MgONWs. Anticancer activity of MgONWs against breast cancer cell lines, namely, Ahmed Murtatha Jabria-13 (AMJ-13) and human breast epithelial (HBL) cells were investigated, and their antimicrobial activity against gram-positive bacteria staphylococcus aureus (S. aureus) was estimated. Contrary to HBL cells, MgONWs showed important cytotoxicity against AMJ-13 cell line. While, antibacterial activity illustrated that S. aureus was influenced via MgONWs. The results proved that MgONWs could be used to treat cancer and bacteria.