In this study, polydimethylsiloxane (PDMS) and NaY zeolite doped composite membranes were prepared for the films varying from 0 to 15 NaY zeolite wt %. All the membranes were characterized by attenuated total reflectance-Fourier transform infrared (FTIR), X-ray diffraction, scanning electron microscopy, thermogravimetry/differential thermal analysis methods. The FTIR spectral results showed that there is physical interaction existing between the PDMS matrix and NaY zeolite. Additionally, film formation from the pure PDMS and PDMS/NaY composites were investigated by photon transmission technique. Activation energies corresponding to the void closure and the interdiffusion stages were calculated. The NaY zeolite added films led to the significant improvement in the mechanical properties that both the tensile strength and Young's modulus increased three times. Thermal properties of the films were also investigated and the addition of NaY zeolite into the PDMS matrix could significantly improve the thermal stability of the composite membranes. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48549.