Two research groups conducted experiments on the mechanical properties of granular materials of plant origin in two distant laboratories without mutual knowledge about running similar projects. Recently established cooperation of a Spanish research group led by Ayuga and Polish research group led by Horabik allowed for in-depth comparison of results. Materials tested in two locations were: wheat, lentils, rapeseeds, sugar and wheat meal. Material characteristics determined were: strength properties (the angle of internal friction, j and the cohesion, c), the modulus of elasticity, E and the Poisson’s ratio, n. Test equipments applied were: direct shear, triaxial compression and uniaxial compression apparatuses. In general, analysis of results of testing in the two laboratories have shown that to obtain consistent results strict concordance in material state, equipment and test conditions is necessary. To resolve the problem standardization of parameters and methods of their determination should be undertaken on an international level.