Abstract. With the diversification of the natural gas origin and the variations of the gas composition, the accurate determination of the gas calorific value is very important in the natural gas industry and the national standardization. A new reference gas calorimeter is developed by KRISS in Korea based on the isoperibolic principle. In this principle, a gas burner is placed in the calorimeter vessel filled with water and the calorimeter is placed in the constant temperature water bath. Methane, oxygen, argon gas are injected in the gas burner and the combustion takes place for 30 minutes. The temperature variation of the water in the calorimeter vessel is measured by Pt25 thermometer. Electrical heater coils around the heater and simulates actual combustion process to find the heat capacity of the whole calorimeter vessel. The gas burner is usually made of pyrex glass but it has the disadvantages of the brittleness and irregular manufacturing. A metal burner is first invented and applied in this study to achieve precise manufacturing and standardization as well as the hardness. A calorific value of methane is measured with the developed gas calorimeter and the result shows within 0.4% difference between the experiment and the reference.