A unique way to control the size and antibacterial activities of silver nanoparticles (Ag NPs) using three different leaf conditions (fresh, oven-dried and sun-dried) of Alstonia scholaris has been reported in this paper. The extract of the A. scholaris leaf acts both as a reducing and stabilizing agent in the formation of Ag nanoparticles. The characteristic surface plasmon peak (415 nm), X-ray diffraction (XRD) studies and energy dispersive spectroscopy (EDS) confirmed the formation of crystalline green Ag nanoparticles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that there was a difference in size for the Ag NPs synthesized from different leaf conditions. Antibacterial studies with both Gram-positive and Gram-negative bacteria showed that Ag NPs synthesized from the fresh leaves displayed the best antibacterial activity, which can be attributed to the size effect of the nanoparticles. © 2016 Elsevier B.V.