Abstract: Quasi-static tensile experiments were performed on the epoxy-based syntactic foams filled by hollow ceramic microspheres with different volume fractions in this study. The effects of microspheres volume fraction on the Young's modulus and Poisson's ratio of syntactic foams were investigated. Microstructure based three-dimensional unit cell models were constructed to capture the stress/strain fields in mesoscale. Cohesive elements were introduced to the FE model to simulate the mechanical behavior of the interface between the microspheres and the matrix material. To verify the validity of the proposed model considering the interface effect, numerical results and two classical analytical methods were compared with the experimental data. It can be found that the ideal interfacial bonding hypothesis based FE model and the classical analytical methods seriously overestimates the experimentally determined Young's modulus and Poisson's ratio. The elastic properties of syntactic foams heavily depend on the mechanical properties of the interface, and only the results obtained by the FE model considering the interfacial effect are much closer to the experimental values and thus provide more accurate predictions.