In this work, we have synthesized Bi2S3 nanoparticles (NPs) by facile chemical precipitation method. The reaction conditions were optimized in order to obtain high yield in a short time. The nanoparticles were synthesized at different pH values ranging from 0.5 to 1.6 and the effect of pH on the growth was investigated. XRD, Raman spectroscopy, SEM, HRTEM, XPS - UV-Vis spectroscopy, and Seebeck were used for the characterization of the nanoparticles. The XRD patterns and Raman analysis revealed the formation of orthorhombic Bismuthunite without any impurity phases. The crystal size of the samples was found to decrease with the increase in pH. SEM images showed that NPs synthesized at pH lower than 1.2 are nanorods and tend to agglomerate as microspheres. At pH 1.6, morphology changes from nano-rods to nano-flakes, and from micro-spheres to micro stems decorated with nano-branches. A possible growth mechanism for the observed pH dependent morphological change is discussed. The estimated band gap energy is in the range of 1.35-1.42 eV. The thermoelectric measurements showed n-type conductivity and high Seebeck coefficients for Bi2S3 NPs. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.