In this study, nano-TiO₂ sulfonated with 1,3-propane sultone (STiO₂) was incorporated into the chitosan (CS) matrix for the preparation of CS/STiO₂ nanocomposite membranes for fuel cell applications. The grafting of sulfonic acid (–SO₃H) groups was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis and energy-dispersive X-ray spectroscopy. The physicochemical properties of these prepared membranes, such as water uptake, swelling ratio, thermal and mechanical stability, ion exchange capacity and proton conductivity, were determined. The proton conducting groups on the surface of nano-TiO₂ can form continuous proton conducting pathways along the CS/STiO₂ interface and thus improve the proton conductivity of CS/STiO₂ nanocomposite membranes. The CS/STiO₂ nanocomposite membrane with 5 wt% of sulfonated TiO₂ showed a proton conductivity (0.035 S·cm⁻¹) equal to that of commercial Nafion 117 membrane (0.033 S·cm⁻¹). The thermal and mechanical stability of the nanocomposite membranes were improved because the interfacial interaction between the -SO₃H group of TiO₂ and the –NH₂ group of CS can restrict the mobility of CS chains to enhance the thermal and mechanical stability of the nanocomposite membranes. These CS/STiO₂ nanocomposite membranes have promising applications in proton exchange membrane fuel cells.