In this paper, Sumudu Transform Series Decomposition Method (STSDM) for solving Integro-Differential Equation is presented. The method is an elegant combination of Sumudu Transform method, series expansion and Adomian polynomial. Three numerical problems were solved and compared with the exact solutions and the results by other approximate methods in order to check the effectiveness, reliability, accuracy, and the convergence of the method. The results obtained by STSDM showed that it is a powerful mathematical technique for solving wide range of physical problems arising in science and engineering fields.