The effects of incorporation of fluorinated alkyl side groups into polyimide membranes were investigated in terms of their physical and gas permeation properties. Four polyimides with fluorinated side groups and four polyimides without the side groups were prepared by polycondensation of 2-(perfluorohcxyl)ethyl-3, 5-diamino benzoate (PFDAB) and m-PDA with four aromatic dianhydrides (6FDA, ODPA, BTDA, and PMDA), respectively. It was found that the incorporation of fluorinated side groups into the polyimide membranes decreased their surface free energies (T(g)s), solubility parameters, and fractional free volume (FFV)s and therefore, enhanced the permeabilities for CO2, O-2, N-2, and CH4 gases but reduced the selectivities for CO2/ CH4, O-2/N-2, CO2/N-2 gas pairs depending upon the structure of dianhydride monomers.