The hemp fiber/polyethylene (PE) composites were prepared by varying the fiber shape (hemp flour and hemp fiber from thermomechanical refining), coupling agent (maleic anhydride grafted and copolymerized onto PE), coupling agent loading method (during fiber treating process in the thermomechanical refiner and compositing process in twin screw extruder), and compositing method (twin screw extruding and batch mixing). The paper firstly measured the moisture absorption properties of the treated fibers. The introduction of coupling agent during fiber treating process decreased effectively the moisture uptake. Then, the water absorption and mechanical properties were investigated on the hemp/PE composites. The loading of coupling agent during fiber treating process decreased the water uptake but also decreased the flexural yield strength, consequently resulted in lower flexural yield strength after water exposure. The composites prepared by batch mixing method were better than by twin screw extruding for the water resistance and mechanical properties. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013