The time-temperature superposition principle was applied to the viscoelastic properties of a kenaf-fiber/high-density polyethylene (HDPE) composite, and its validity was tested. With a composite of 50% kenaf fibers, 48% HDPE, and 2% compatibilizer, frequency scans from a dynamic mechanical analyzer were performed in the range of 0.1-10 Hz at five different temperatures. Twelve-minute creep tests were also performed at the same temperatures. Creep data were modeled with a simple two-parameter power-law model. Frequency isotherms were shifted horizontally and vertically along the frequency axis, and master curves were constructed. The resulting master curves were compared with an extrapolated creep model and a 24-h creep test. The results indicated that the composite material was thermorheologically complex, and a single horizontal shift was not adequate to predict the long-term performance of the material. This information will be useful for the eventual development of an engineering methodology for creep necessary for the design of structural building products from these composites. (C) 2005 Wiley Periodicals, Inc.