The basic characteristics of stress-strain-temperature relation were investigated experimentally as research on the mechanical properties of shape memory polymer of polyurethane series. The main results are summarized as follows. (1) The deformation resistance of the material increases with the number of cycles under the cyclic deformation at temperatures above glass transition temperature. (2) If training is performed before the practical use and the maximum strain is smaller than 100%, the constant recovery strain may be obtained under thermomechanical cycling. (3) The strain obtained at low temperature following the predeformation given at high temperature does not vary under thermomechanical cycling, which shows stable shape fixity of the material for the cyclic deformation.