We establish a condition for the existence and uniqueness of a periodic solution of a system of nonlinear integro-differential equations with pulse action. The solution is represented as the limit of periodic iterations. We give estimates for the rate of convergence and for the exact solution of the system.The problem of the existence of periodic and bounded solutions of a system of integro-differential equations in noncritical cases was studied in [1,2]. The application of the Bubnov-Galerkin method to the construction of periodic solutions of systems of integro-differential equations was considered in [3]. The numerical-analytic method for the investigation of periodic solutions [4] was used for the construction of periodic solutions of a system of integro-differential equations in [5]. Periodic solutions of systems of integro-differential equations with pulse action were found in [6].In the present paper, using a constructive method [7], we establish conditions for the existence of periodic solutions of systems of integro-differential equations with pulse action at fixed times in nondegenerate and degenerate cases. We construct periodic solutions of weakly nonlinear integro-differential equations in nondegenerate and degenerate cases and consider possible distributions of pulse conditions. In each case, we construct iterations, which are determined from integral equations, and propose an algorithm for the determination of approximations in explicit form.Consider the system of integro-differential equations