This paper presents a new approach for radial distributed network planning with using ACO algorithm. Ant colony optimization algorithm (ACO) is one of the best methods for optimization in difficult discrete problems. The new algorithm determines the optimal configuration of network and voltage level of each section of the feeders and calculates the optimum rating of the transformers and the size of each section of the feeders. This algorithm applied to a real 23-feeder radial test network of

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... an Regional Electricity Company inIran. The results validate the superiority of new algorithm in comparison with particle swarm optimization (PSO) and supplying area algorithm. The important characteristics of this algorithm in this paper are its high speed in solving problems for instance 240 times of supplying area algorithm time and 18 times of PSO algorithm time and 10% decreasing of final cost because of considering the transformers rating as an another searching space variable.