Biosynthesis of Ag and Ag-CuO nanoparticles using aqueous leaf extracts of Mimosa pigra is presented. The nanoparticles were synthesised using different concentration ratios of aqueous leaf extract of Mimosa pigra to the silver and copper salts. The nanoparticles were characterised using UV–vis spectroscopy, fourier transform infra-red (FTIR) spectroscopy, powder X-ray diffraction (PXRD), scanning and transmission electron microscopies. Stable nanoparticles with average particle size of 17.5 nm (Ag) and 49.5 nm (Ag-CuO), which were capped by the plant extracts via the O-H and C=O groups from flavonoids, tannins and other biocompounds were obtained. The UV-vis spectra revealed earlier formation of surface plasmon bands for silver nanoparticles when the volume of extract was reduced, although with lower intensity. In the spectrum of Ag-CuO nanoparticles, broad bands around 400-500 nm appeared in the region of 365–369 nm. Crystallite size of approximately 50 nm for the Ag-CuO was calculated from XRD results using Schererr’s equation and the particles were well dispersed as shown by the TEM images. The photocatalytic activities of the synthesized Ag and Ag-CuO nanoparticles were studied towards the degradation of methylene blue (MB) and hydrogen peroxide (H2O2). The results provide eco-friendly reaction toward environmental remediation from common pollutants