In the past two decades, gas separation by polymeric membranes has been extensively developed due to their inherent advantages, such as low cost, high energy efficiency and ease of operation. However, the application of polymeric membranes is limited by the trade-off between permeability and selectivity. Recently, mixed matrix membranes (MMMs) with combined advantages of polymeric matrix and fillers have been widely attentioned to overcome this limitation. In this study, polysulfone MMMs incorporated with cyanuric chloride, melamine and 2,4,6-trihydrazino-1,3,5 triazine were prepared using the phase inversion method. The effects of fillers loading (0–2 wt.%) on the membrane characteristics were studied using scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR); while the gas traort properties were investigated using pure gas permeation tests of N 2 , O 2 , CO 2 and CH 4 at 10 barg and 30 ? C. Formation of non-selective voids at the polymer-filler interface region was observed due to poor adhesion between polymer and filler in the case of cyanuric chloride and melamine fillers. However, Well dispersion of 2,4,6-trihydrazino-1,3,5 triazine particles in the polymer matrix was observed. The obtained gas permeation results showed that in the nano composite membrane containing 2%wt cyanuric chloride particles, the permeability of carbon dioxide, oxygen, nitrogen and methane gases increased strongly as 59.93%, 86.14%, 342.79% and 404.16%, while selectivities of CO 2 /CH 4 , CO 2 /N 2 and O 2 /N 2 decreased on average 68%, compared to pure Psf. Also, in the nanocomposite membrane containing 2%wt melamine fillers, permeability of carbon dioxide, oxygen, nitrogen and methane gases increased as 25.40%, 17.21%, 79.74% and 94.69%, while selectivities of CO 2 /CH 4 , CO 2 /N 2 and O 2 /N 2 decreased on average 36%, compared to pure Psf. The most optimum sample is the membrane with 2 wt.% of 2,4,6-trihydrazino-1,3,5 triazine loading, which exhibited improved CO 2 permeability of 38.76% and CO 2 /N 2 and CO 2 /CH 4 selectivities of 74.37% and 58.45%, respectively, compared to other samples. Keywords: Polysulfone Membrane, Cyanuric Chloride, Melamine, 2,4,6 Trihydrazino-1,3,5 Triazine, Mixed Martix Membrane, Gas Separation.