In this work, the biomolecule-assisted microwave heating synthesis of ZnIn2S4, along with the ZnIn2S4/MoS2 composites and their photocatalytic applications, were studied. Well-defined flower-like ZnIn2S4 microspheres synthesized at microwave heating time of 1 h provided the highest surface area and total pore volume, which offered the highest H2 production rate (111.6 μmol h-1 g-1). Different amounts of MoS2 were loaded into the ZnIn2S4 microspheres to form ZnIn2S4/MoS2 composites aiming to improve the H2 production rate. Among the fabricated ZnIn2S4/MoS2 composites, the ZnIn2S4/MoS2-40% wt composite exhibited the highest H2 production rate (200.1 μmol h-1 g-1) under UV-visible light irradiation. In addition, for the first time, this composite was applied for the photoreduction reaction of Cr(vi) ion under visible light irradiation. It provided higher photoreduction efficiency than the single components, where the efficiency was improved in the acidic solutions over the levels recorded in the basic solution. The charge transfer pathway and photocatalytic mechanisms of the ZnIn2S4/MoS2-40% wt photocatalyst have been proposed based on the results obtained from UV-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy, Mott-Schottky measurements and the silver photo-deposition experiment.