Renewable Energy Source (RES) is unreliable because it fluctuates by itself. This problem can solve by Battery Energy Storage System (BESS) installation. Installation of BESS in each place cause different effects for the micro grid. This paper proposed a method for optimal location and optimal sizing to install BESS in a micro grid using Particle Swarm Optimization (PSO) technique. Wind power and solar power were the primary sources of power generation in this study. The IEEE standard 14 bus system was used, and the system was simulated via the MATLAB program. The simulation results showed that the installing of BESS at an optimal location reduced the consumption of power loss in the microgrid. Optimal size installation provided the ability of charge and discharged power enough to all load to maintain the voltage all bus in a day. Also, reduced the cost of investment from the un-optimal size of the BESS installation.