Copper nanoparticles (CuNPs) are having profound interest in the present tremendous research due to their exquisite fascinating spectrum of physical and chemical properties along with their significant potential activity in a very wide range of applications. In the present study, CuNPs were synthesized through simple chemical reduction method and studied the effect of pH disparity on particle size variation. The X-ray diffraction analysis confirmed the formation of cubic structured CuNPs with high crystalline nature. The morphological study ascertains the formation of CuNPs with spherical shape and without any agglomeration. With pH increment the particle size was observed to be decreased due to increased reactivity. Energy dispersive spectroscopy results attested the presence of metallic copper. UV-Vis absorption spectra of CuNPs show single maximum absorption band which confirms the spherical shaped NPs formation. The antibacterial activity was carried out against Escherichia coli and Pseudomonas spp. The CuNPs showed more antibacterial activity against Pseudomonas spp. than E. coli. At last, the synthesized CuNPs size can be tuned with pH variation and small sized nanoparticles exhibited higher antibacterial activity. © 2016 Elsevier Ltd.