Quaternized SiO₂ (QSiO₂) was firstly prepared by modification of nano-sized SiO₂ using silane coupling agent with quaternary ammonium groups. And then, a series of quaternized chitosan-poly (vinyl alcohol)/QSiO₂ (QCS-PVA/QSiO₂) interpenetrating polymer networks (IPN) composite membranes were fabricated by adding QSiO₂ into the QCS-PVA blend matrix and followed by glutaraldehyde crosslinking. The structure, thermal stability and ionic conductivity of the composite membranes were characterized by FT-IR, SEM, thermogravimetric analysis (TG) and electrochemical impedance spectroscopy (EIS). The results show that the thermal stability of the composite membranes is significantly improved. The ionic conductivity of QCS-PVA/QSiO₂ composite membranes exhibits a trend of rise first then fall. The QCS-PVA/QSiO₂ composite membranes with 5% QSiO₂ show the highest ionic conductivity as high as 0.0644 S/cm, which is about three times of the ionic conductivity of the pure QCS-PVA membrane (0.022 S/cm) at room temperature, indicating the potential application of these composite membranes in fuel cells.