The micro-grid has been operating at institute of technology of Shimizu Corporation since July, 2006. Main generators are two gas engine CHP systems which capacity are 350kW and 90kW. Two power storage devices, secondary battery and electric double layer capacitor, are also installed to compensate rapid load fluctuation. In this paper, load demand is analyzed by using frequency analysis and this sampling interval is decided by probability distribution of power transition. DG systems' characteristics such as frequency response, fuel efficiency and frequency stabilization capability are also assessed. Capacity of DG Systems in the Micro-grid is evaluated by results of load demand analysis and DG systems' characteristics assessment.