PURPOSE: A composition useful as fibers easily dyeable with cationic dye, having low melting point, obtained by blending a tetramethylene terephthalate polyester with a copolymer polyester copolymerized with a metal sulfonate-containing compound.

CONSTITUTION: 100pts.wt. polyester consisting of tetramethylene terephthalate as a main constitutional unit, having ≥0.6 intrinsic viscosity, is blended in a molten state with 2W100pts.wt. copolymer polyester (preferably ≤240°C softening point) copolymerized with at least 5wt% metal sulfonate-containing compound [especially, sodium 3,5-di(carbomethoxy)benzenesulfonate], having ≥0.1, preferably 0.15W1.0 intrinsic viscosity under heating (≤280°C) without causing ester exchange as much as possible. The amount of sulfonate group is 10W500 equivalents based on 1 ton total polymer composition, and a catalyst in the polymer is preferably deactivated to suppress the ester exchange.