Abstract: Complicated microstructures of 3 D woven fabric composites are described by structural and geometric parameters; flattened yarns are represented by lenticular geometry. A methodology based upon fabric microstructure is developed to predict the fiber volume fraction and elastic constants of 3 D woven fabric composites. Parametric analyses were performed to examine the effects of various structural and geometrical parameters on the elastic properties of the 3 D composite. A code with user friendly interface has been developed to provide an efficient calculation tool in selecting the best fabric reinforcement for structural composites. A comparison of the resulting analytical predictions with experimental data shows that the proposed model is correct.