This paper deals with the results of three dimensional compression tests carried out for high stiffness urethane foams (Penguin-foam, Sunstar Engineering Ltd.), and also deals with the constitutive modelling base on Shima-Oyane’s consolidation condition for the tested foamed urethane. Three kinds of urethane foams, relative densities of which were 0.1, 0.2 and 0.33, were employed in the experiments. Like metallic porous materials, the tested urethane foams show the strong plastic-compressibility. On the other hand, in modelling, unlike metallic porous materials, the identified material constants for different density foams do not take the same (or unified) values but take the different values when Shima-Oyane’s constitutive model is assumed. Furthermore, the experimentally derived stress-relative density curves could not be satisfactorily described by Shima-Oyane’s original constitutive model; the experimental stress-relative density curves show stronger work hardening as compared with the simulated ones especially in the large deformation stage. To avoid those inconvenience, in this paper, a modified Shima-Oyane type constitutive equation was also proposed, and it was shown that the proposed model could well express both the low work hardening area of the stress-relative density curves at the initial deformation stage and the strong work hardening area at the final deformation stage by supposing the stress restriction at initial deformation stage due to the buckling of cell walls of each foam, and the rapid stress increase at the large deformation stage caused by the successive contact and the friction between the bent cellular walls, respectively.