Thermal decomposition of unmodified poly(vinyl alcohol) (PVA) and poly(vinyl alcohol) crosslinked with sulfosuccinic acid (SSA) membranes has been studied using thermogravimetry (TGA) and ATR Fourier transform infrared spectroscopy (ATR-FTIR). Both types of membranes degrade in a two-step process. However, the introduction of SSA leads to an advance of the decomposition steps at very low temperatures. The reduction in the hydrogen-bond interactions of hydroxyl groups of unmodified PVA because of the presence of SSA crosslinks and the catalytic effect promoted by sulfonic acid group (–SO3H) of SSA can contribute to this different behavior. The kinetics of thermal degradation was investigated by TGA and derivative TGA (DTGA) curves from experiments under non-isothermal conditions at different heating rates. The Friedman isoconversional differential method was used to calculate the activation energy as a function of the reaction weight loss without any previous assumption on the kinetic model. For a representative stage of decomposition, preexponential factor and kinetic model were also obtained. Postcuring isothermal treatments and ATR-FTIR analysis of selected membranes have been used to verify the TGA analysis and add additional information.