Zinc oxide (ZnO) and Cu-doped ZnO nanoparticles (1% and 5%; Cu-doped ZnO NPs) were synthesized using aqueous leaf extract of Stachytarpheta jamaicensis. Crystalline ZnO and Cu-doped ZnO NPs with hexagonal wurtzite structure were obtained without any impurities as confirmed by powder X-ray diffraction. The optical properties, morphology, elemental composition, and surface analysis of all the samples were studied using UV-vis diffuse reflectance spectroscopy, scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDX), and X-ray photoelectron spectroscopy, respectively. Antibacterial activities of the ZnO and Cu-doped ZnO were performed by screening test at the highest concentration (500 mg/mL) against two gram-positive bacterial strains (Bacillus subtilis and Staphylococcus aureus) and two gram-negative bacterial strains (Pseudomonas aeruginosa and Escherichia coli). Antibacterial activities were observed only against gram-positive bacteria. Minimum inhibitory concentration (MIC) ranged from < 25 to 50 mg/mL.