Triaxial tests were performed on wheat flour to determine the constitutive parameters for a modified Cam-clay model. This elastoplastic model consists of three critical-state parameters : lambda, kappa, and M. Additionally, there are two parameters representing the initial conditions of a material : e0 and p(c). All critical-state parameters were determined directly from four different triaxial tests : drained compression, undrained compression, constant mean effective stress and hydrostatic compression. The material parameters for the tested wheat flour, following standard statistical techniques, were : lambda = 0.13, kappa = 0.022 and M = 2.1. The model was tested by comparing model-calculated deformation under triaxial loading conditions identical to those used to determine the parameters. The comparisons between the modified Cam-clay model calculated values and measured values showed that drained triaxial compression tests and constant mean effective stress tests were within the 95% confidence interval. The investigation proved that (1) standard triaxial tests and constitutive models can be successfully applied to dry, cohesive powders, and (2) constitutive parameters defined in soils models can be determined for dry powders by modifying the parameter determination procedure.