Continuum level modeling of damage is a complex problem because of existence of several failure mechanisms at various length-scales, e.g., matrix crack, interfacial crack and delamination. Several macroscopic models have been proposed in the literature for the characterization of the influence of these damage modes. However, very few models account for the micro-level mechanisms. Further, most micromechanical models are two-dimensional (2D) in nature. Hence, the effect of finite size and orientation of the damage is not captured. The present work focuses on developing a generalized macro level damage model for unidirectional composites based on the micromechanical analysis in the presence of finite sized damages. The effect of microdamage mechanisms is modeled through effective stiffness reduction at a macro point. A series of numerical experiments, based on the mathematical theory of homogenization, have been conducted at the level of the constituents to obtain the effective stiffness properties for the Representative Volume Element (RVE) with existing damage. The effect of various damage mechanisms, size and mode of damage on effective macro properties is studied and definitive conclusions are drawn. The dependency of these effects on the volume fraction is also studied. Based on the conclusions, a generalized macro level damage model is proposed. © 2008 Trans Tech Publications.