Distributed generation is the process of generating electricity from small energy sources and connecting it to the distribution network or on the customer's side of the meter. The placement of distributed generation and the size of the distribution generation is important. Determining the optimal location and sizing of a Distributed Generation (DG) Unit is being presented in this paper. The radial distributed network has been considered. A robust stochastic optimization technique based on the movement and intelligence of swarms called Particle Swarm Optimization has been implemented to obtain optimal solution of the DG placement problem. Reduction of line losses in the radial distribution network is the main objective of this paper. © 2012 IEEE.