PURPOSE: To obtain liquid crystal-forming polyesters that will provide a polyester molded item, particularly, a fiber or a sheet that has a high strength and a high Yound'g modulus, by introducing substituents having specific sizes in specified quantities to aromatic rings.

CONSTITUTION: Polyesters consisting of compounds of the formulaeIWIV (wherein lWn each are 0 or a positive integer provided that 1≤l+m+n≤4 should be satisfied, and XWZ which may be the same or different each represent a radical with a valance of 1 provided that when the numbers of atoms other than hydrogen in the radicals are designated x, y and z respectively, 2≤nx+ my+lz≤8 should be satisfied) in such a ratio of 20W60mol% compoundI, 5W 20mol% compound II, 5W35mol% compound III and 20W40mol% compound IV is heated to a melted liquid crystal state, and is extruded. This may be subjected to heat treatment at a temperature ≥150°C under tension or a slackened condition. Thus fibers or films can be obtained.