Chitosan (CS) modified graphitic carbon nitride (g-C3N4)/ZIF-8/PES membrane was synthesized for enhancement in CO2/CH4 separation. The layer by layer growth method of membrane fabrication was applied for the synthesis of ZIF-8 on polyethersulfone (PES) support. The samples were characterized by XRD, gravimetric analysis of crystallinity degree, laser particle size distribution analysis (PSD) and SEM to investigate the crystal structure and morphology of ZIF-8. The FTIR and 13C NMR spectroscopies were applied to investigate the formation of possible bonds between g-C3N4 and ZIF-8 respectively. Pure gas permeation tests showed that the chitosan modified g-C3N4 incorporated ZIF-8 membranes have superior CO2/CH4 ideal selectivity (24.2) compared with pristine ZIF-8 membrane. Due to the approved formation of C[sbnd]N bond between g-C3N4 and imidazole group of ZIF-8, the flexibility of the modified ZIF-8 membrane increased remarkably. The mixed gas permeation test results showed the same trend of change of pure gas tests but with reduced values of CO2 and CH4 permeances and CO2/CH4 selectivities especially for CS/g-C3N4/ZIF-8 membrane due to the significant competing effect in penetration of gases in this membrane sample. © 2019 Elsevier B.V.