The cyclic loadings during mastication supposedly accelerate degradation of soft lining materials. The purpose of this study was to investigate the effects of cyclic loading on viscoelastic properties of soft lining materials. Two plasticized acrylics, two silicones and one isoprene-based monomer contained elastomer were selected. Cylindrical-shaped specimens, 10 mm X 10 mm phi, were prepared. Twenty specimens were subjected to cyclic loading in a water bath at 37 degrees C; another twenty specimens were without cyclic loading. The viscoelastic properties were measured using a creep-meter. The cyclic loading significantly decreased the heights of the two materials, the instantaneous elastic displacements of one acrylic liner and the viscous flows of three materials. The cyclic loading affected mainly delayed deformations. Therefore, cyclic loading was a useful method for evaluating the durability of soft lining material.