Penetration of distributed generation (DG) units in distribution systems are attracting the researchers nowadays. Number, Capacity, and situation of DG units have a significant role affecting the performance of a distribution network. This paper presents a novel technique based on Grey Wolf Optimizer (GWO) which is applied to the optimal number, size, and location of DG units to minimize the active power loss and improve the voltage pro le of radial distribution networks. GWO will be compared with Genetic Algorithm (GA) optimization method to show the superiority and effectiveness of the proposed technique. In this paper, performance analysis is carried out considering IEEE 33-bus and 69-bus test radial distribution systems.