Abstract: The tensile and compressive experiments of the polyurethane syntactic foams filled by hollow glass micro-spheres with different densities and mass fractions of micro-spheres were carried out to investigate the influence of micro-spheres on the mechanical properties. The experimental results show that the features of the tensile curves for the filled syntactic foams are similar to those of the conventional foams. However，the compressive characteristics of stress-strain relation of the filled syntactic foams differ from those of the conventional foams. With increasing of the material density，the micro-spheres have better reinforced effect on the resin matrix. It is found that the micro-sphere cluster and bad bonding at the interface between the  micro-spheres and the resin would probably lead to the decline of mechanical properties. According to the simulation results using the finite element method and the observation of the damaged samples，the deformation and failure mechanism of the material were discussed.