Abstract The deformation behavior of two phase composites containing coarse rigid particles in ductile, plastically deforming matrices has been investigated using a simple, continuum mechanics model. The model has been derived on the basis of a unit cell, representative of the composite microstructure, which is idealized to a pattern of periodic cubic inclusions distributed uniformly in a continuous plastically deforming matrix. The stress-strain behavior is arrived at by dividing the unit cell into elements of matrix and inclusion and accounting for the constrained deformation of matrix while ensuring strain compatibility. The resulting closed form expressions have been used to predict the flow stress and stress-strain behavior of composites. The predictions have been compared with specific examples of deformation of composites for which numerical solutions, data from finite element calculations as well as from experiments are available. Typical composites considered include discontinuous particle reinforced composites and transversely loaded continuous fiber composites. A good agreement between the model predictions and data from finite element and numerical simulations as well as experimental measurements is found.