Nickel oxide nanoparticles (NiO NPs) were synthesized via a green route using Abrus precatorius seed extract as a natural reducing and stabilizing agent. The produced NiO NPs were physicochemical characterized using ultraviolet–visible (UV–vis) spectroscopy, revealing the characteristic absorbance peak at 320 nm. SEM revealed nanoparticles with nearly spherical to polyhedral morphologies and a tendency to agglomerate, typical of green synthesis . Energy-Dispersive X-ray Spectroscopy (EDX) confirmed Ni (55.76 wt%) and O (32.75 wt%) as the major elements, validating the formation of NiO. Dynamic light scattering (DLS) analysis showed an average particle size of 166.9 nm with a Poly Dispersity Index (PDI) of 0.340, indicating moderate uniformity. Thermogravimetric analysis (TGA) showed ∼20–25 % weight loss due to organic decomposition, confirming the thermal stability and purity of the calcined NiO NPs. In vitro antioxidant assays indicated that NiO NPs exhibited dose-dependent activity; however, their scavenging efficiency at 250 μg/mL (49.3 %) was lower than that of ascorbic acid (AA) (70.6 %). Antimicrobial evaluation using agar well diffusion showed stronger inhibition against Bacillus subtilis and Escherichia coli than against Aspergillus flavus , Klebsiella pneumoniae , and Staphylococcus aureus , with activity increasing dose-dependently up to 200 μg/mL. The findings highlight that A. precatorius seed extract not only enables eco-friendly synthesis but also enhances the biological functionality of NiO NPs, supporting their potential as antimicrobial agents and pharmaceutical candidates, particularly against antibiotic-resistant pathogens. © © 2025. Published by Elsevier B.V.