Nanotechnology is a relatively revolutionary area that generates day-to-day advancement. It makes a significant impact on our daily life. For example, in parasitology, catalysis and cosmetics, nanoparticles possess distinctive possessions that make it possible for them in a broad range of areas. We utilizedMollugo oppositifoliaL. aqueous leaf extract assisted chemical reduction method to synthesize Co3O4nanoparticles. Biosynthesized Co3O4Nps were confirmed via UV–Vis spectroscopy, scanning electron microscope, X-ray diffraction, EDX, Fourier-transform infrared, and HR-TEM analysis. The crystallite size from XRD studies revealed around 22.7 nm. The biosynthesized Co3O4nanoparticle was further assessed for mosquito larvicidal activity against south-urban mosquito larvaeCulex quinquefasciatus, and antimicrobial activities. The synthesized Co3O4particle (2) displayed significant larvicidal activity towards mosquito larvaeCulex quinquefasciatuswith the LD50value of 34.96 µg/mL than aqueous plant extract (1) and control Permethrin with the LD50value of 82.41 and 72.44 µg/mL. When compared to the standard antibacterial treatment, Ciprofloxacin, the Co3O4nanoparticle (2) produced demonstrates significantly enhanced antibacterial action against the pathogensE. coliandB. cereus. The MIC for Co3O4nanoparticles 2 againstC. albicanswas under 1 μg/mL, which was much lower than the MIC for the control drug, clotrimale, which was 2 µg per milliliter. Co3O4nanoparticles 2, with a MIC of 2 μg/mL, has much higher antifungal activity than clotrimale, whose MIC is 4 μg/mL, againstM. audouinii.