This paper describes the operating condition of 1.5MW gas engine system with pyrolysis gas produced in the waste gasification plant. This system started since Octorber 2001 at Kawasaki-Steel chiba works. The results shows the following four conclusions; (1) Gas engine can operate continuously with pyrolsis gas of which LHV is between approximately 1500 and 2200kcal/m^3_N, enen when the fluctuation of LHV is approximately 3%/30s. (2) Electrical efficiency is 37% at 100% load and 33% at 50% load respectively. (3) The concentration of dioxins in the exhaust gas was approximately 0.001ng-TEQ/m^3_N. (4) The concentration of NO_x in the exhaust gas is less than 100ppm (O_2=0%) without SCR.