Abstarct: Reliability is one of the most important issues in electrical power systems and distribution systems respectively. Achieving high reliability indices in distribution networks, is a key factor which is considered by system engineers and energy suppliers to assure providing the demanded energy of consumers as well as increasing the profit of power distribution companies. Switch placement is one of the most effective methods of reliability improvement in distribution systems. Considering the growing role of distributed generation (DG) in the current and future of the power systems, the major challenging issue in switch placement is to find the proper locations of switches in distribution systems when the DGs are present. In this project a new graph-theory and improved genetic algorithm baxsed practical method is employed to solve a multiobjective optimization problem. The proposed method determines the best locations of switching devices in distribution networks considering the effects of presence of distributed generation in fitness functions and other optimization constraints, providing the maximum number of costumers to be supplied by distributed generation sources in islanded distribution systems after possible faults . The proposed method is applied and simulated on several distribution test systems in both cases of with DG and non DG situations. The results of the simulations validate the proposed method in switch placement of the distribution network in the presence of distributed generation.