Membrane technologies are among the newest gas separation technologies and today they are widely used in various oil, gas and petrochemical industries. Among different membranes being used in gas separation, polymeric membranes are used more extensively. But creating a balance between selectivity and permeability is one of the major problems of pure polymeric membranes. Using mixed-matrix membranes is a method to overcome this limitation. Mixed-matrix membranes possess necessary capacity to achieve a higher level of selectivity and permeability or both, compared to available polymeric membranes. In this study, we initially used the cyanuric chloride compound which has chlorine polar groups in its structure, in order to make poly(urethane-urea) mixed-matrix membranes. Then, by changing particles’ structure, by adding some active amine groups to it and converting it to melamine and 2, 4, 6-Trihydrazine and 1, 3, 5 Triazine (THDT), we studied the effect of adding these groups on the performance of mixed-matrix membranes, in the process of gas separation. All the membranes were prepared by using phase inversion method and through applying solvent evaporation. Pure and mixed-matrix membranes were then evaluated by using XRD, FT-IR and SEM techniques. The result showed that all three particles distributed uniformly through the membrane and there is good compatibility between particles and polymer phases. According to FT-IR test result's the presence of Cyanuric Chloride particles in hard segments and THDT and Melamine particles in soft segments of polyurethane is more likely. Also, the permeability of carbon dioxide, oxygen, methane and nitrogen were measured at the pressure of 10 bar and at 30 ° C temperature for all the pure and Mixed Matrix Membranes. Comparison of permeability of gases in Mixed Matrix Membranes shows that poly(urethane-urea) /Cyanuric Chloride Mixed Matrix Membrane has had the most rate of permeability improvement in comparison with the pure membrane; so that the permeability of carbon dioxide, oxygen, methane and nitrogen, which were respectively 83.44, 7.26, 11.72 and 3.48 in pure poly(urethane-urea) membrane increased to 132.68, 10.73, 14.24 and 4.90 in poly(urethane-urea) / Cyanuric Chloride Mixed Matrix Membrane containing 10 wt% of Cyanuric Chloride and thus they have increased 59%, 48%, 22% and 21% respectively. The largest increase in the selectivity belonged to poly(urethane-urea) /THDT Mixed Matrix Membrane in which the selectivity of a pair of gases, including carbon dioxide to methane, carbon dioxide to nitrogen and oxygen to nitrogen increased from 7.12, 24.00 and 2.09 in pure poly(urethane-urea) a membrane to 12.46, 46.14 and 2.40 in 10wt% poly(urethane-urea) / THDT mixed matrix membrane and they increased 75%, 92% and 15% respectively. Keywords : Polyurethane, Mixed Matrix Membrane, Cyanuric Chloride, Melamine, 2, 4, 6-Trihydrazine-1, 3, 5 Triazine, gas separation.