The elastic modulus of polymeric membranes based on PVOH + H3PO2 + TiO2 was studied as a function of relative humidity (%RH) and the volumetric fraction of water. Tensile stress-strain tests (nominal stress) were performed to determine Young's modulus, yield strength, break stress, and strain stress at a constant speed of 10 mm/min. The membrane’s acid concentration was kept constant at the molar concentration of high proton conduction P/OH = 0.3, and they were separated into two test groups, 5 wt. %TiO2 fillers, and without TiO2. For relative humidity between 8 and 94% RH, the membranes with TiO2 show an improvement in the elastic modulus concerning those without TiO2 doping, but they have no significant difference at 100% RH, under a confidence level of 95%. In general, the data analysis indicates that the mechanical properties and the electrical properties of the membranes previously reported are directly related to the absorption of water contained in the hydrophilic groups that expand during swelling. In contrast, the hydrophobic solid-like polymer backbone and the TiO2 nanoparticle fillers maintain structural stability.