Textile composites are suitable for applications in lightweight structures, since they provide an assessable composite strength and stiffness. Furthermore, the textile preforms offer a high drapability as well as a good impact behaviour of the composite material. Novel textile reinforcement systems such as unique biaxial reinforced weft knitted fabrics are composed of biaxial reinforcing layers that are held together by a 3Dstitching yarn system. Reinforcing yarns, e. g. glass fibres or carbon fibres can be used within all yarn systems. Especially the failure behaviour and the phenomenology of damage of those new textile reinforced composites have been barely investigated so far. In this paper, the damage behaviour of the biaxial reinforced weft knitted composites is studied based on experimental measurements. The failure modes and the resulting degradation of the mechanical properties are evaluated by carrying out a series of tensile tests using acoustic emission techniques to detect the crack distribution of [0/90]s and [+45/-45]s GF/EP composites. Subsequently, a phenomenological plane stress damage mechanics based model for these composites has been developed. Damage variables are introduced to describe the evolution of the damage state and as a subsequence the degradation of the material stiffness. Special emphasis is given to the interaction between fibre failure due to fibre stress and matrix failure due to transverse and shear stress. The performance of the model strongly depends on the correct determination of the material parameters. Thus, the damage parameters and their evolution laws are determined having regard to the performed experimental crack density studies. By means of micromechanical models, the reduced stiffness properties of the damaged [0/90]s composites can be found depending explicitly on the crack densities of the damaged layers. The results of the theoretical damage model show good agreements compared to the experimental test data and provide a useful framework for further development of the proof of design of highly loaded structures made of textile reinforced composites.