This paper discusses the conceptual development of unit cell (UC) approach in modeling the total deformation and failure response of quasi-brittle composites. The UCs were modeled with only two distinct phases, namely the volume fractions of the matrix phase and that of the inclusion phase, for the mechanical characterization of the materials under consideration. A study has been carried out to determine the minimum size of the UC, above which the predicted response may be size independent, making it a representative unit of the four quasi-brittle composites considered. The minimum size required was observed to be higher than that of a pure deformation model, and the results varied with the total volume fraction of the constituent phases. The failure strength predicted by the UC of a particular volume fraction was also compared with that of the corresponding experimental results, resulting in a good correlation between the two. © 2014, Springer-Verlag Wien.