An electrochemical sensing platform made of a reduced graphene oxide-silver (rGO-Ag) nanocomposite was developed for the detection of 4-nitrophenol. The synthesis of the nanocomposite was monitored at different reaction times (2 h, 6 h, 10 h and 15 h) in modified Tollens' test and characterized using UV-visible absorption spectrum, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy analyses. Completely spherical Ag nanoparticles (NPs) were found at a reaction time of 15 h with an average particle size of 16 nm. The nanocomposites prepared with different reaction times were used for the electrocatalytic reduction of 4-NP, and the rGO-Ag (15 h) nanocomposite-modified glassy carbon (GC) electrode displayed a higher faradaic current at an overpotential of -0.5 V toward 4-NP reduction. The rGO-Ag (15 h) nanocomposite-modified electrode was used for the square wave voltammetric (SWV) detection of 4-NP in a 0.1 M phosphate buffer (pH 7.2), and it showed a good sensitivity toward 4-NP detection even for a nanomolar concentration. The nanocomposite exhibited multi-linear ranges and 4-NP detection limit was found to be 1.2 nM. The present sensor was stable and selective to 4-NP in the presence of its structural analogues such as 2-nitrophenol (2-NP), 2-aminophenol (2-AP), 3-aminophenol (3-AP), 4-aminophenol (4-AP), and 2,4-dichlorophenol (2,4-DCP). The rGO-Ag nanocomposite could be successfully applied for the determination of 4-NP in real water samples, and good recoveries were found. (C) 2016 Published by Elsevier Ltd.