Explosive characteristics of the city gas were determined by using the gas explosion apparatues. The explosive range is determined between lower explosive limit of 5.0% and upper explosive limit of 15.3% at atmosphere and even though the oxygen concentration is decreased, lower explosive limit is not changed, but upper explosive limit is rapidly decreased. The minimum oxygen for combustion is determined 10%. The maximum explosion pressure is determined 5.72$ extrm{cm}^2$ and the maximum rate of explosion pressure rise is oxygen concentration of 12% to determined 160.12$ extrm{cm}^2{cdot}$sec.