The present invention relates to a drawn PET fiber that can provide a cap ply cord and the like showing more improved modulus and good dimensional stability, a PET tire cord, and a tire including the same. The drawn PET fiber may be a fiber including 90 mol % or more of PET, of which the crystallinity is 53% or more, the amorphous orientation factor (AOF) is 0.15 or less, and the birefringence index is 0.14 to 0.16, after heat-treating the same at 230° C. for 1 minute under the initial load of 20 g/1000 d.