The effects of phosphoric acid (p) on the polyvinyl alcohol (PVA) as highly hydroxyl-group content polymer have been investigated. Functionalized membranes (p-PVA) have been prepared via sol-gel method with different doped acid ratios. Fourier Transform Infrared (FTIR) spectroscopy is used to confirm the structure of the pure polymer and the synthesized membrane. Water uptake capacity, plane swelling, thickness swelling, proton conductivity by electrochemical impedance spectroscopy (EIS) and thermal stability by thermal gravimetric analysis (TGA) are used to characterize the membranes for their applications in the suitable engineering fields. The results showed that the doped acid has suppressed effects on the hydrophilic properties of the used polymer which leads to decreasing in the water uptake and swelling properties of membranes. Thermally cross-linked 30% p-PVA thin membrane was selected because of its good water uptake capacity (43.78%) and low swelling degree (21.07%). The proton conductivity of all membrane increased with increasing the temperature up to 60 degrees C for 30% p-PVA thin membrane and it attained to 0.07 S cm(-1). The proton conductivity decreased to 0.013 S cm(-1) at the same temperature for 40% p-PVA thin membrane. The thermal stability of doped polymer membranes is significantly higher than pure hydroxylated polymer which indicates the strong bonding between the doped acid and polymer. (C) 2019 Elsevier Ltd. All rights reserved.