Abstract: An experimental investigation was conducted to characterize the mechanical behaviors and failure criterion of engineered cementitious composites (ECC's) subjected to biaxial compression by using a triaxial electro-hydraulic servo test system. ECC cubic specimens with three different strength grades were tested in the experiments. The failure modes, ultimate strength and stress-strain curves of ECC's under biaxial compression were obtained and compared with those of conventional concrete. Then, the failure mechanism and variation law of principal compressive strength were analyzed. The test results demonstrated that the strength envelope curves of ECC's were different from the curves of conventional concrete under biaxial compression. The strength envelope curves of the two kinds of materials are close when the strength is low. But with increasing strength, the increase of principal compressive strength of ECC's was apparently less than that of ordinary concrete. Finally, based on the Kupfer's strength criterion for conventional concrete and test results, a novel failure criterion was proposed for ECC materials under biaxial compression.