We investigated relations between diffusivities on polyimides and physical parameters with mobilities of segments and examined viscoelasticity of polyimides on introducing the parameter as an index of mobilities of polymer chains. Each relaxation temperature of viscoelasticities on polyimide films having ordered regions was almost the same as that on the amorphous states. The CF, group as a substituent showed the similar effect to that of CH, group in elastic relaxation. The storage modulus was correlated well with the gas diffusivity. And in the case that relations between the diffusion coefficients and cohesive energy densities (CED) which were introduced as an index of cohesiveness of segments, the relation between CED and the gas diffusivities showed a good correlation. Mobilities of segments affected strongly the gas diffusivities even in the glassy polymers such as polyimides.