Abstract: A device for the chemical treatment of fiber surface was designed and installed, with which UHM PE fibers were treated continuously. Unidirectional composites of treated UHMPE fiber/epoxy resin were manufactured. The short beam shear strength of the composites was measured in order to evaluate the effect of fiber treatment. The compressive, flexural and impact properties were also tested and the results show that this type of composites is extremely tough though its stiffnesses and streng ths are lower than those of carbon fiber reinforced composites. The main failure modes of this material include debonding and delamination, fiber buckling and bending, instead of fiber breaking usually observed in carbon or glass fiber reinforced composites.