In this paper, synthesized Fe₃O₄ nanoparticles applied as catalyst in photodegradation of Direct Red 23 (DR23) dye using photo-Fenton process in aqueous solution. The Fe₃O₄ nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Design of experiments (DOE) based on Taguchi approach was used. Analysis the response of each experiment was based Signal to Noise (S/N) ratio was calculated. The effective parameters for the degradation of dye were determined and optimized using Taguchi (L₉ (3⁴)) orthogonal array experimental design method with four factors having three levels for each factor. The Taguchi approach showed that pH 3 (level 1), catalyst amount = 25 mg/L (level 2), H₂O₂ concentration = 15 ppm (level 3), and temperature = 35°C (level 3) was optimum conditions for this process. The factor most influencing the process was determined using analysis of variance (ANOVA) method. The most significant factor in this process was pH. The interaction between pH × catalyst amount was the most influencing interaction. The percent (p (%)) of each factor on the degradation of dye was found to be in the following the order: pH (50.306%), catalyst amount (6.887%), H₂O₂ concentration (39.272%), and temperature (3.456%). The percentage contribution of factors in this process was found to be in the following the order: pH (0.332), catalyst amount (0.101), H₂O₂ concentration (0.291), and temperature (0.082). So first order reaction with k = 0.0472 min^–1 was observed for the photocatalytic degradation reaction.