The tensile stress relaxation and flexural creep properties of wood-fiber-reinforced low-density polyethylene (WFRP) were measured at various temperatures and stress levels. Power law relations were used to correlate the data, and time-temperature superposition was applied to tensile stress relaxation results. Stress relaxation in WFRP was similar to that of IDPE and greater than that in spruce. The clamping force and torque characteristics of self-threading screws and internally threaded inserts were measured in WFRP, and the viscoelastic model was extended to predict the relaxation in screw clamping force as a function of time. Both screw pullout force and the amount of clamping force relaxation were greater in WFRP than in spruce.