The elastic modulus E(1) of the crystalline regions in the direction parallel to the chain axis was measured by X-ray diffraction for a number of ethylene-vinyl alcohol (EVA) copolymers with various vinyl alcohol (VA) contents. Although the E(1) values of polyethylene (235 GPa) and poly(vinyl alcohol) (250 GPa) are very high, these copolymers possessed much lower E(1) values. The change in the E(1) values of the copolymers with VA content could be expressed by a parabolic curve with a minimum value of 79 GPa (VA = 40.0 mol %). This tendency corresponded well to the change in the fibre identity period where the EVA copolymer (VA = 40.0 mol%) shows the most contracted skeletal. These results could be explained with a kinked-chain model where a contracted portion was introduced into the chain, with the latter bringing about the low E(1) value for the EVA copolymer. The E(1) value for the EVA copolymer (VA = 62.0 mol%) increased from 108 GPa at 25 degrees C to 226 GPa at - 150 degrees C. The contracted portion was considered to be introduced into the chain by thermal vibrations, even at room temperature.