In this study, Fe-alloyed CdZnS nanoparticles (NPs) with 1% Fe concentration (Fe (1%): CdZn (2%)S) were synthesized by chemical precipitation at room temperature. The synthesized NPs were used as a catalyst for the decomposition of methylene blue under UV light. The obtained results showed that the photocatalytic activity of Fe (1%): CdZn (2%)S NPs was higher than that of CdZn (2%)S NPs. It was determined that the kinetics of the photocatalytic degradation of the methylene blue (MB) correspond to the pseudo-second order kinetics model. In addition to the photocatalytic properties, the structural, morphological and optical properties of Fe (1%): CdZn (2%)S NPs were investigated.