Three kinds of polyester fibers were treated with NaOH to modify their properties. Through the alkaline hydrolysis, the physical and morphological properties were studied. All fabrics of three fibers decreased in tearing strength with loss in weight, but showed the same value at the same loss in weight regardless of treating temperatures and alkaline concentration. At the early stage of alkaline treatment the tearing strength decreased steeply, but leveled off as hydrolysis proceeded. After alkaline treatment many microvoids were produced on the surface of fiber, and this was enhanced by delustring agent. The yarn containing delustring agent had more voids than that of no delustring agent due to alkaline treatment. The dye uptake of regular polyester fiber was not changed with dyeing temperature, but in case of easy shrinkable copolyester and conjugated polyester it showed the maximum value at 12$0^{circ}C$. The dye uptake of conjugated polyester fiber increased, but K/S value decreased because of scattering effect.