Highly stable nanoparticles of metallic silver with average dimension of 26.6 nm were synthesized by a simple, cost-effective, reproducible and previously unexploited biogenic source viz. dried green fruits of Drypetes roxburghii (Wall.) (common name putranjiva). The as-synthesized silver nanoparticles (Ag NP) were characterized by their characteristic surface plasmon resonance absorption spectra, X-ray diffraction analysis, energy dispersive X-ray analysis and selected area electron diffraction study. The morphology of the particles was determined by high-resolution transmission electron microscopy. Fourier transform infrared analysis focuses some light on the chemical framework that stabilizes the nanoparticles. The analyses of the phytochemicals present in the fruit extract of the plant were also performed following standard protocol. Mosquito larvicidal bioassay with the Ag NPs was carried out with two mosquitoes, namely Anopheles stephensi Liston and Culex quinquefasciatus Say. The results show impressive mortality rate even at too low concentration of nanoparticle. Toxicity test on non-target organism shows no harmful effect during the study period.