TiO2/WO3 nanocomposites (NCs) were successfully prepared by ultrasonic-assisted sol-gel method and acid functionalized (sulfated) by using chlorosulfonic acid. Various physicochemical properties of as prepared NCs were studied by using X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy with energy dispersive analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, UV visible diffused reflectance spectroscopy, and Brunauer-Emmett-Teller (BET) surface area analysis. It was confirmed that the active sulfonic groups are anchored onto the surface of binary NCs. Furthermore, the photocatalytic performance of this material was significantly higher for the degradation of Congo red and methyl red dyes. Both these azo dyes were degraded only within 120 min under visible light irradiation. Recyclability of this catalyst was also studied and it was found that even after five consecutive cycles the introduced catalyst retain its catalytic efficiency above 90%. •Binary TiO2/WO3 NCs prepared by ultrasonic-assisted sol-gel method.•NCs were sulfated by using chlorosulfonic acid as a precursor.•Anchoring of sulfonic groups was revealed by FT-IR, EDX and XPS techniques.•Sulfonic groups retard electron-hole recombination as confirmed by PL spectroscopy.•Sulfated NC proved efficient visible active photocatalyst for azo dyes degradation.