© 2017, Hanyang University. All rights reserved. ZnIn 2 S 4 microspheres were synthesized via a hydrothermal method using zinc chloride (ZnCl 2 ), indium chloride tetrahydrate (InCl 3 ·4H 2 O) and L-cysteine (C 3 H 7 NO 2 S). The effect of hydrothermal temperatures (160°C, 200°C and 240°C) on the crystallinity, morphology and optical properties of the synthesized powders was investigated. The synthesized products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The results showed that the synthesized powders were pure ZnIn 2 S 4 with a hexagonal structure. The ZnIn 2 S 4 powders were microspheres with diameters of 8.3-9.5 µm, constructed from several nanosheets. These nanosheets interconnected with each other, forming a pore structure. With increasing hydrothermal temperature, the nanosheets increased in thickness and the width of the pores between the nanosheets expanded. The ZnIn 2 S 4 powder synthesized at 240°C exhibited stronger UV-Vis absorption and photoluminescence (PL) intensities than the other samples. The photocatalytic activity of the ZnIn 2 S 4 photocatalyst was investigated by photodegradation of methylene blue under blue light irradiation; 97% of the methylene blue degraded within 210 min. Photostability of the ZnIn 2 S 4 photocatalyst was also investigated.