A simplified continuum damage mechanics model is proposed to describe the inelastic behavior of concrete reinforced with randomly distributed short fibers. The constitutive and damage behavior of such a concrete usually involves anisotropic damage, unilateral effect, coupled volumetric and deviatoric inelastic deformation and complicated failure mechanisms due to its heterogeneous morphology. In order to avoid the analytical and computational complexity, a scalar damage variable is adopted, while the anisotropy and unilateral effect of damage corresponding to different states of stress and stress histories are described through introducing the Lode parameter lr. The proposed model can take into account the effect of fiber content on damage development and the effect of volumetric stress on deviatoric inelastic response. The validity of the proposed model is demonstrated by comparing the theoretical and experimental results for plain and fiber-reinforced concrete specimens subjected to triaxial stress histories. The in uence of fiber content on the response of concrete subjected to cyclic loading histories and on the fatigue life is also analyzed.