Cubic beta-In2S3 nanoparticles (NPs) have been synthesized by a simple and facile way, which is 6 nm in size. Absorption and emission spectra of In2S3 NPs show obvious blue peak shift compared to band gap of bulk In2S3, indicating the strong quantum size confinement effect. The fluorescence quantum yield of In2S3 NPs is found to be 10%. During the synthesis process, the absorption spectra have no peak shift, which is responding to transition from valence band to the conduction band levels. This absorption spectra show that the nucleation and growth process of In2S3 NPs is very quick. The PL lifetime spectra and time resolved spectra give two emission processes in In2S3 NPs, which would be excitonic recombination and electron-hole recombination via defects levels. The blue shift of emission peaks show the emission process in In2S3 NPs is from mainly electron-holes recombination via defects levels to excitonic recombination. The Stokes shift becomes smaller which is mainly contributed by blue shift of emission and smaller contribution from the UV-Vis absorption. The absorption and emission spectra show the size and crystallinity of In2S3 NPs have no changes (HRTEM images provide enough proofs); however the surface-related defects changed greatly in the reaction process. (C) 2010 Elsevier Inc. All rights reserved.