A B S T R A C TWastewaters originating from dyes production and application industries pose a major threat to surrounding ecosystems because of their toxicity and potentially carcinogenic nature. In this study, the removal of a reactive azo dye called Magenta MB (MMB) was done by photo-Fenton process using heterogeneous Fe 3 O 4 catalyst and homogeneous FeSO 4 catalyst. The effect of different system variables namely catalyst concentration, H 2 O 2 dosage, pH, and initial concentration of the dye were studied. The influence of inorganic salts and ligands in the photo-Fenton system were examined. The stability of Fe 3 O 4 catalyst has also been determined. The homogeneous photo-Fenton system exhibited the highest removal efficiency of 96.7% under the operating conditions of catalyst concentration of 300 mg L −1 , H 2 O 2 dosage of 9 g L −1 , initial pH of 2.5, and concentration of MMB of 50 mg L −1 . The optimum operating condition as per the experimental results for the heterogeneous photo-Fenton system, while using Fe 3 O 4 catalyst is 500 mg L −1 of catalyst dosage and 6 g L −1 of H 2 O 2 dosage for 50 mg L −1 of initial dye concentration at an initial pH of 2.5 in 90 min with a dye removal efficiency of 94.9%. The addition of salts and ligands were found to be having an inhibiting effect on the Fenton system. Results showed that magnetite was found to be an efficient photo-Fenton catalyst for dye removal.