Constitutive modelling of the stress-strain relationship of open-celled PLGA 85/15 bioscaffolds under compression was studied. A constitutive model for compressive behaviour was directly derived from the morphology of a unit cubic cell. These constitutive equations describe the stress-strain relationship as a function of the foam's material properties and cell morphology, such as elastic modulus, yield stress, relative density, cell strut thickness, and cell size. To verify this model, uniaxial compression testing was performed on scaffold samples. Using the gas foaming/salt leaching method, the samples were prepared by using different foaming parameters such as salt/ polymer mass ratio, saturation pressure, and saturation time. The comparisons of theoretical and experimental data demonstrate that the constitutive model using a cubic unit cell accurately describes the behaviour of PLGA foams with low relative densities under compression.