The water absorption pattern and associated dimensional changes and solid loss of oil palm fiber-linear low density polyethylene composites was studied. The effects of fiber size (425-840, 177-425, and 75-177 mu), fiber loading (0, 10, 20, 30, 40, and 50%), and time of immersion (192 h at an interval of 24 h) on these parameters were also studied. Alkali treatment of fibers was done to reduce the hydrophilic nature of the composites and its effect was studied. It was found that the water absorption in most of the combinations followed typical Fickian behavior. The rate of water absorption and swelling increased with fiber loading. However, alkali treatment of the fibers resulted in a reduction of water absorption at higher fiber loadings only, and composites with higher fiber sizes exhibited higher water absorption. A sharp increase in the thickness swelling was observed in the initial days of immersion, which remained constant thereafter. The thickness swelling also increased with fiber size; however, a constant trend was not observed for the 75-177 mu fiber size. In addition to thickness swelling, composites also expanded linearly during water absorption; however, linear expansion was considerably less than thickness swelling. Higher fiber loading and alkali treatment caused more linear expansion. We observed that maximum solid loss on water immersion occurred with small-sized and also alkali-treated fiber composites. An increase in thickness and a decrease in linear dimension were observed after one sorption-desorption cycle. This irreversible change was also found to be proportional to fiber loading and alkali treatment. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1064-1075, 2010