This manuscript reports the fabrication of polyethersulfone (PES)/ polydimethylsiloxane (PDMS)/zeolitic imidazolate framework (ZIF-L) composite membrane for gas separation. ZIF-L is a new type of nanosheet metal-organic frameworks that can selectively separate CO2. Hypothetically, its presence in the selective layer will simultaneously improve CO2 permeance and selectivity. The effect of four parameters (PDMS concentration, withdrawal speed, holding time and ZIF-L:PDMS ratio) involved during the fabrication process on the separation performance were thoroughly looked at. Except for ZIF-L:PDMS ratio, it was found that, all parameters have a significant influence on both, the thickness of selective layer and amount of ZIF-L present. ZIF-L:PDMS ratio has substantial impact on the ZIF-L adhered on the support. The ideal fabrication condition was 3 wt% PDMS concentration, 5 mm/s withdrawal speed, 120s holding time and 1:1 ZIF-L:PDMS ratio. At these conditions, the composite membrane recorded 4.25 GPU, 15.71 GPU and 8.93 GPU of CO2 permeance, CO2/N2 and CO2/CH4 selectivity, respectively.