Moisture uptake and desorption response of a high fiber volume fraction pultruded carbon/epoxy composite is studied through immersion of specimens in deionized water at three temperatures. It is seen that uptake response is best characterized by a two-stage model indicating an initial diffusion based response followed by a relaxation and deterioration based response. Desorption and short-term resorption responses are Fickian in nature and show the clear effect of prior history. The ratios of longitudinal to transverse diffusivity of desorption indicate a decrease with increasing level of initial temperature of immersion in deionized water. These values are significantly higher than those listed in the literature for lower fiber volume fraction composites, and are attributed to the high levels of fiber loading, with local areas of fiber-to-fiber contact. Viscoelastic characterization through dynamic mechanical thermal analysis clearly differentiates between plasticization and further network/interface deterioration based phenomena.