The present study reported a facile and rapid biosynthesis method for gold nanoparticles (GNPs) silver nanoparticles (AgNPs) and bimetallic heterogeneous sliver-aurum nanoparticles(AgAuNPs) using the leaves of Gmelinaarborea (ROXB) (Family Verbenaceae) extract. The aqueous leaves extract was used as biotic reducing and stabilizing agent of the growing nanoparticles. The synthesized gold nanoparticles (AuNPs),silver nanoparticles (AgNPs) and silver-gold core-shell nanoparticles(AgAuNPs) were characterized using UV-Vis spectroscopy (UV–Vis), Fourier transform infrared spectroscopy, (FT-IR), X-ray diffraction (XRD),transmission electron microscopy (TEM)and thermal gravimetric analyses (TGA). Several factors such as the extract amount, contact time and solution pH, as possible influences; were investigated to obtain the optimized synthesis  conditions. The antimicrobial activity study revealed that while the aqueous extract at concentrations of0.8 and 4% (w/v) showed no effect on the antimicrobial activity, the produced nanoparticles, AuNPs, AgNPs and AgAuNPs inhibited thegrowth of Gram positive bacteria (Bacillus subtillus, Staphylococcus aureus), Gram negative bacteria (E. Coli and Pseudomonas aeruginosa) and Fungi (Candida albicansand Aspergillusniger). The cytotoxic activity against hepatocellular carcinoma (HePG2)was alsoevaluated.