In this article, we present a new numerical method to solve the integro-differential equations
(IDEs). The proposed method uses the Legendre cardinal functions to express the approximate
solution as a finite series. In our method the operational matrix of derivatives is used to
reduce IDEs to a system of algebraic equations. To demonstrate the validity and applicability of
the proposed method, we present some numerical examples. We compare the obtained numerical results from the proposed method with some other methods. The results show that the proposed algorithm is of high accuracy, more simple and effective.