Within the framework of this thesis, an analysis and optimization of MV distribution networks with interconnection of DG units have been introduced. In the first part, investigations of the impacts of DG unit''s interconnection on the loadability of MV distribution networks are introduced. In the second part a new methodology for integration of the DG units in order to enhance the voltage limit loadability is presented. In the third part, investigations on the implications of Distributed Wind Power Generation (DWPG) on voltage ranges, voltage profiles, and energy losses of a real MV distribution network are introduced. In the last part of the thesis, a new methodology for optimal reconfiguration of a typical MV network with the existence of different DG technologies is presented. The proposed methodology implementing C++ and NEPLAN software is developed for optimizing the switching state of the network where the load and generation profiles are taken into consideration. The objective function of the proposed algorithm is minimizing the energy losses. The VDEW standard load profiles for households and commercials are used in the simulation.