The chalcogenide composite FeIn 2 S 4 was prepared by hydrothermal route and, for the first time, investigated as a heterogeneous catalyst in the photo-Fenton treatment for Ponceau 4R dye (C 20 H 11 N 2 Na 3 O 10 S 3 ) under visible irradiation. The composite was characterized by X-ray diffraction (DRX), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDS) and elemental mapping, band gap energy and X-ray photoelectron spectroscopy (XPS). The optimal experimental conditions were investigated and determined to be pH 3.0, 0.5 g L −1 of catalyst and 2.5 mmol L −1 of H 2 O 2 . A decolorization efficiency of 93.3% was achieved in 60 min of reaction and a TOC removal of 92.3% was reached in 180 min. The stability and recycle capacity of FeIn 2 S 4 indicated that the catalyst can be used more than four times without considerable loss of efficiency. Free radicals investigation revealed that • OH and O 2•− radicals were the major oxygen reactive species involved on Ponceau 4R degradation. The lower-mass intermediates from Ponceau 4R degradation were identified, and a mechanism for the photo-Fenton treatment was suggested. Therefore, the composite showed a performance that makes it a promising catalyst for removing emerging contaminants in water.