Abstract: A textured polyester yarn having improved variation in dyeability along its length is composed of a plurality of individual filaments each having thick and thin sections randomly distributed along the filament axis, said yarn having an Uster evenness value of 1.0 to 10.0%, a T index of 3 to 30 and a variation in reflected light intensity in a continuous dyeing test of .+-.0.15 to .+-.0.80 and said yarn preferably having not-untwisted portions containing genuine twists of a fixed direction intermittently retained at random along its length. The yarn is produced by false twisting a polyester yarn composed of a plurality of individual filaments each having variation in cross-sectional area along its length, in which the thick sections have a birefringence of 15 to 80.times.10.sup.-3 and the thin sections have a birefringence of 90 to 200+10.sup.-3, at a temperature of not lower than 180.degree. C and under a twisting tension of 0.05 to 0.8 g/d with a variation with respect to the average twisting tension of .+-.