Ag2ZnSnS4 (AZTS) nanoparticles were successfully synthesized at relatively low temperature via thermal reaction of corresponding metal acetates and a sulfur source in a hot oleylamine solution, the purity of the particles being dependent on the amount of metal acetates and the reaction temperature. The obtained pure AZTS particles with size of ca. 15 nm exhibited photoresponse with visible light irradiation similar to that of n-type semiconductors.