The aim of this study is to investigate the influence of EPS content on failure mode, stress-strain relationship and elastic modulus of expanded polystyrene aggregate concrete (PAC) with density lower than 900 kg/m3 under uniaxial loading. The results show that PAC performs a good compressibility in the compression failure process. Apparent oblique crack appears in the case of uniaxial compression specimen damage; the lower the density is, the smaller the tilt angle of oblique cracks will be. Stress-strain curve of PAC with density larger than 422 kg/m3 maintains a straight line relationship on ascending segment but varies with the density on the descent segment. The lower the density is, the larger PAC residual relative stress will become. Elastic modulus of PAC is proportional to 5.85 times index of relative density.