In this paper, the optimization of micro-cogeneration (μ-CHP) system sizing for convenience stores in Thailand is conducted under the present condition of fuel prices and tariff rates. The assessment of (μ-CHP) system performance is analyzed by using Primary Energy Saving (PES) Ratio for evaluating the energy performance. Also, the Annual Cost Saving Ratio (CSR) and Payback Period (PBP) are used for evaluating the economic performance of μ-CHP system. The analysis results show the optimal size of μ-CHP system under possible conditions including the operating schedule and system’s efficiency were conducted.