In general, permeability and diffusivity in crystalline and liquid crystalline polymers are thought to decrease with increasing crystallinity. However, according to our statistical literature data analysis with 300 of crystalline and liquid crystalline polymers, permeability and diffusivity of carbon dioxide, oxygen, and nitrogen were not significantly affected by crystallinity at the lower crystallinity ranges. Some of them were observed with almost constant or slightly increased values of the permeability and diffusivity at the lower crystallinity range. In contrast, finally, at a higher crystallinity, gas permeability and diffusivity decreased. No increase in the solubility is observed for crystalline and liquid crystalline polymers, regardless of the crystallinity. The crystalline structure could form discontinuously in crystalline and liquid crystalline polymers at a lower crystallinity. The crystal structure gradually grew like a phase transition from the discontinuous domains with increasing crystallinity. At a higher crystallinity, the crystal structure might effectively prevent the diffusion of gas molecules because the crystal structure could be changed from discontinuous to continuous crystal domains after phase transitions. Therefore, gas permeability and diffusivity began to diminish after the phase transition of the crystal structures. (C) 2010 Elsevier B.V. All rights reserved.