A theoretical model for the evaluation of the elastic modulus in particulate composites has been developed. The method takes into account the contiguity of the particles and also the existence of an interphase between main phases, which constitutes an important parameter influencing the behavior of a composite material. This layer between the matrix and filler develops different physico-chemical properties from those of the constituent phases and variables along its thickness. The effect of the progressive variation of the elastic modulus of the interphase on the modulus of the composite was estimated by assuming a law of variation. The theoretical values derived from the proposed model were compared with experimental results carried out on iron-particulate-filled epoxy composites and with theoretical values derived from models of other scientists. This comparison was proved to be satisfactory for our proposed model.