Carbon nanotube (CNT)-modified SrTiO₃/Fe₂TiO₅ nanocomposite was synthesized as a novel heterojunction photocatalyst by a co-precipitation method. The composition of SrTiO₃ with Fe₂TiO₅ and incorporation of CNT in the composite decreased the mean particle size from 70 to 45 nm, reduced the band gap energy from 3.2 to 2.82 eV, and increased the surface area about 3 times greater than the pure SrTiO₃. The valence band X-ray photoelectron spectroscopy (VB-XPS) and UV–visible diffuse reflectance spectroscopy (DRS) results demonstrate that SrTiO₃ and Fe₂TiO₅ phases effectively formed a charge transfer mechanism of type-II heterostructure. The lower intensity of photoluminescence (PL) spectroscopy peak, augmented photocurrent density, and less resistance of charge transfer indicated that the ternary SrTiO₃/Fe₂TiO₅/CNT nanocomposite has a more significant charge transfer efficiency in comparison with pure SrTiO₃ phase and binary SrTiO₃/Fe₂TiO₅ nanocomposite. The prepared composite exhibited excellent photocatalytic activity and degraded the methylene blue dye completely. Using response surface methodology (RSM) method for experimental design, the optimum amounts of irradiation time, initial dye concentration and catalyst dosage of 71 min, 13.2 mg/L and 1.32 g/L were obtained, respectively. After four cycles, the photocatalyst showed high reusability and stability. The synthesized nanocomposite exhibited lower degradation efficiencies for Rhodamine-B and methyl orange dyes.