This paper presents the effectiveness of the particle swarm optimization (PSO) to minimize the total active power loss of an island scale micro grid distribution network. In the adopted method, the co-simulation of the PSO algorithm and the Mat-power software on an island scale electrical network was proposed. The power system in Kiribati is selected as the study case. Two diesel power generation stations, one voltage regulator unit and one switching shunt capacitor bank are used to regulate the system voltage. The 24-h load flow is executed with the proposed PSO algorithm to minimize the active power loss and the annual power loss savings can be estimated. It is concluded that the proposed PSO algorithm can work well and give a satisfactory result.