Wide-angle x-ray diffraction studies were performed for as-spun wet poly(p-phenylene terephthalamide) fiber. The effects of sorbed water on the equatorial diffractions from the (110) and(200) crystal planes and on the meridional diffractions from the (002), (004), and (006) crystal planes were analyzed during desorption and absorption. There was no significant change in the d-spacing from the respective crystal plane irrespective of the moisture (water) regain. The ratio of the diffracted intensity from the (110) diffraction to that from the (200) diffraction remarkably increased by removing the sorbed water. The crystallite size estimated from the (110) diffraction, L-110, also increased as the moisture regain decreased, while the L-200 did not increase. The longitudinal size of paracrystallite, D-001, also remarkably increased with the decrease in moisture regain with the lattice distortion factor, g(II), kept unchanged. These results strongly suggested the growth of the crystallite via hydrogen bonds in the lateral (b-axis) direction. The growth of the lateral size of crystallite also accompanied the longitudinal growth of crystallite during desorption.