In general, the effective properties of a n-phase composite material can be calculated by considering an (n+1)phase composite model, where the (n+1)-phase consists of the equivalent homogeneous composite material. In the present study a three-phase composite which consists of spherical inclusions, an interphase and a matrix is considered. The effective properties of this three-phase composite can be calculated exactly using the four-phase composite model, and also by applying the less complicated three-phase composite model twice, in succession. Here by applying these two methods to a typical composite, elastic properties of the interphase can be determined from the properties of the inclusion, matrix and composite. It is seen that the three-phase composite model yields results, which are very close to the results obtained from the four-phase composite model. ___________________________________________________________________________________________