The properties of oil palm fiber were estimated and compared with oil seed flax and industrial hemp fibers. Biocomposite of oil palm fiber and linear low density polyethylene (LLDPE) was manufactured. The effect of fiber size, fiber content and fiber treatment on dimensional stability of the biocomposite was studied. The true density of oil palm fiber is found to be 1503 kg m-₃. The oil palm fibers obtained from field contained nearly one-fourth impurities, and the equilibrium moisture contents (EMC) values of fibers nearly doubled with 25% increase in relative humidity. The dielectric constant of oil palm fiber was in the range of 7.76-8.31. The oil palm fiber resulted in thermograms with two endothermic peaks and three exothermic peaks with the first degradation temperature at 301.71°C. Alkali treatment reduced first degradation temperature to 297.1°C. The specific heat capacity of oil palm fiber varied from 1.083 J g-₁ °C-₁ to 3.317 J g-₁ °C-₁ in the temperature range of 20°C to 150°C. A sharp increase in composite thickness swelling upon immersion in water was observed in the initial days of immersion, which maintained constant thereafter. The thickness swelling increased with fiber size. In addition to thickness swelling, composites expanded linearly also during water absorption, however linear expansion was considerably less than thickness swelling. Higher fiber loading and alkali treatment caused more linear expansion. It was observed that maximum solid loss on water immersion was for small-sized and also alkali-treated fiber composites. Increase in thickness and decrease in linear dimension was observed after one sorption-de sorption cycle. This irreversible change was also found proportional to fiber loading and alkali treatment.