Photo-induced phase transition (PIPT) of CdZnS based nanocomposites that was performed at the room temperature under the solar light illumination is reported here for the first time. CdZnS particles were decorated on reduced graphene oxide (RGO) with a solvothermal process and consequently RGO-CdZnS-5%Pt nanocomposites (PC) have been synthesized as zinc blende (cubic) phase of CdZnS. Zinc blende structure (cubic) of CdZnS components of PC was turned to wurtzite (hexagonal) crystal structure with PIPT during the photocatalytic hydrogen evolution reaction. The band gap of the photocatalyst decreased from 2.42 to 2.19eV and the hydrogen evolution rate increased from 37.3 to 184.0 mu mol h(-1) due to the PIPT process. [GRAPHICS] .