The structure-property relation of para-aramid fibers heat-treated under various conditions was investigated. The effect of heat-treatment on the mechanical properties of the fibers was also studied. Tensile strength and strain at break decreased and tensile modulus increased with increasing heat-treatment temperature. Tensile modulus also increased with increasing draw ratio. Structural characterization was carried out by using wide angle X-ray scattering (WAXS) method. Both the apparent crystal sizes (ACS) measured from the broadening of reflection peaks of (004), (110) and (200) planes and the orientation angle obtained from azimuthal scan along the (200) direction were found to increase with increasing heat-treatment temperature and draw ratio.