Thermotropic liquid crystalline polyesters and copolyesters based on the 4,4'-dihydroxy-α-methyl stilbene(DYS-00, DYS-50, DYS-70) or 4,4'-dihydroxy-2,2'-dimethyl azoxybenzene(AZA-9 and DDA-9) were processed to obtain films and fibers; The films of these polymers were prepared by the casting of polymer solutions in chloroform and fibers of them were prepared by the melt spinning in their mesophases. The mechanical properties of these films and fibers such as moduli and tenacity were studied. The variation in the moduli of the films as a function of elongation ratio was studied; The moduli of films were increased with elongation ratio. The effect of the temperature on the moduli of the films and fibers was also studied; The moduli of unoriented films decreased in relatively large scale with increasing temperature, but those of oriented films and fibers did not decrease much even above glass transition temperatures.