Abstract: Green synthesis of metal nanoparticles using earth abundant materials in the absence of any toxic solvent, reducing agent and protecting group is one of the emerging areas of research in materials chemistry. Herein, we report a green method for the synthesis of silver nanoparticles (AgNPs) using Actinodaphne madraspatana Bedd leaf extract as reducing as well as stabilizing agent. To our delight, AgNPs of different sizes could be readily synthesized by simply changing the pH of plant extract and the average size of AgNPs were found to be 60, 35 and 20 nm at pH 6, 9 and 12 respectively. The efficacy of prepared AgNPs towards the catalytic reduction of 4-nitrophenol (4-NP) has been investigated and the nanocatalysts have demonstrated excellent catalytic activity as evidenced from the rate constants. The kinetics of reduction reaction follows Langmuir–Hinshelwood mechanism, based on which the rate constant ‘k’ was calculated. The effect of catalyst dosage, concentration of 4-NP, concentration of NaBH4 and size of AgNPs towards catalytic reduction of 4-NP has been systematically investigated. It was interesting to notice that the AgNPs have exhibited size dependent catalytic activity towards reduction of 4-NP and the catalytic activity was found to increase with decrease in particle size. Graphical Abstract: [Figure not available: see fulltext.]. © 2017, Springer Science+Business Media New York.