2,3,5,6-Tetramethyl-1,4-phenylenediamine (TMPD) based polyimide (PI) were crosslinked with 1,2-Diaminoethane(DAE) and 1,6-Diaminohexane (DAH) to enhance gas transport properties. Fourier transform infrared (FT-IR) studiesshow that imide groups were converted into amide groups during crosslinking process. Thermogravimetric analysis (TGA)results indicate that the degradation temperature of crosslinked PI membranes decreased after crosslinking. This is due todegradation of alkyl group in crosslinking agent. The d-space of crosslinked PI membranes decreased with increasing crosslinkingtime. The ideal permeability for CH₄, N₂, O₂, and CO₂ decreased after crosslinking and the ideal permeability ofcrosslinked PI membranes induced by DAH is larger than that by DAE. In contrast, the permselectivity of CO₂/CH₄, CO₂/N₂and O₂/N₂ increased during crosslinking. For the gas pair of CO₂/CH₄, the maximum increment is about 39.5% after 6 minutesof DAE crosslinking. Also, that of O₂/N₂ gas pair is about 20.5% after 6 minutes of DAE crosslinking. According tothese result, DAE is more suitable for enhanced permselectivity than DAH. On the contrary, DAE is not useful for CO₂/N₂separation due to reduction in CO₂/N₂ permselectivity after 3 minutes DAE crosslinking.