The crystal structure of poly[oxy-1,3-(2-cyanophenylene)-oxy-1,3-phenylene] was determined by X-ray diffraction. The structure belongs to the monoclinic system with the space group P2(1)/a, and has unit cell constants of a = 8.62 Angstrom, b = 13.07 Angstrom, c (chain axis) = 9.03 Angstrom and P = 99.0 degrees (second setting). There are four monomer units (i.e. four chains) in the unit cell. The molecules in the crystal are constricted by 0.5 Angstrom per monomeric unit from the fully extended conformation, and the planes of the adjacent benzene rings lie at an angle of similar to 90 degrees to each other. The longitudinal elastic modulus of the crystalline component was estimated to be 44 GPa from the X-ray diffraction measurements. Because the polymer is not fully extended, this elastic modulus is not very high.