Abstract: The polyurethane rigid foamed plastics are important light structural materials. To investigate their shear mechanical properties is quite necessary for their applications.By the low speed torsional experiments of PUR foamed plastics, their shear mechanical behavior has been studied here. With these experiments, their shear properties such as the shear modulus and strength of PUR foamed plastics have been determined. Furthermore, the fracture surface SEM analyses of PUR foamed plastics have also been done to investigate the mechanism of shear failure in foamed plastics. Finally, the theoretical predictions for shear mechanical properties of PUR foamed plastics are given by means of author's theoretical formulae. The predicted results agree quite well with the experimental results. Particularly, some results obtained in this paper are firstly reported.