We synthesized novel fluorinated block copolyimides with various diamine compositions and block chain lengths by chemical imidization in a two-pod procedure. We describe the gas-transport properties of the novel block copolyimide membranes. We demonstrate that the gas-transport properties of the copolyimide membranes strongly depended on the block chain lengths. The gas permeabilities of the copolyimide membranes increased with increasing block chain length, and the gas selectivities increased with decreasing lengths. We clarify that the gas diffusivity of the block copolyimide membrane dominated the gas-transport properties. (c) 2006 Wiley Periodicals, Inc.