Sunlight induced strategy for the rapid green synthesis of silver nanoparticles (AgNPs) is reported for the first time using aqueous leaf extract of Achyranthes aspera. On exposing a mixture of silver nitrate solution and aqueous leaf extract of A. aspera to sunlight, stable silver nanoparticles were obtained within few seconds. The water soluble biomolecules from the A. aspera served as both reducing and capping agents in the synthesis of silver nanoparticles. The nanoparticles were characterized using UV–Vis., Fourier transform infrared (FTIR), transmission electron microscopy (TEM), and EDAX techniques. The pseudo first order rate constant kobs, for the formation of AgNPs was found to be 3.49 x 10 -2 min -1 . The particles were stable for 3 months. The nanoparticles were mono-dispersed, spherical in shape with the average size of 12.82 nm. FT-IR analysis revealed that the -OH groups, possibly, from saponin were responsible for the reduction of silver ions to silver nanoparticles (AgNPs). Thus prepared AgNPs have desirable cytotoxicity towards bacterial strains and fungus and the effect was compared with standard drugs, Amikacin and fluconazole respectively. This green and mild technique can be used for the large scale extracellular synthesis of silver nanoparticles and the AgNPs thus prepared may be used for biological applications.