Novel polyester filamentary yarn is provided having (a) a fineness of 0.9 denier per filament or less, (b) an amorphous orientation in the range of 30% to 70% and (c) a negative .epsilon..sub.0.2 where said .epsilon..sub.0.2 is a structural integrity parameter. The yarn possesses ameliorated properties regarding a heat-setting property, a raising property, a dimensional stability and a twist resistance. The yarn finds its wide range of usage, for example, silky fabrics with an excellent fullness, pliability and liveliness, raised fabrics with thermally stabilized fluffs protruding straight-forwardly and an extremely soft hand, and uniformly creped fabrics with an improved surface contour are obtained therefrom.