The CO2 emission for each process in the Japanese steel industry is estimated by a process analysis using statistical data in order to evaluate the possibility of reducing CO2 emissions. The emission factor of CO2 for each product and also for crude steel produced from an integrated steel plant route and an electric are furnaces route is estimated and compared. The CO2 emissions can be estimated from production amounts of products for each process and for crude steel. The CO2 emission of blast furnaces is the largest and that of rolling and piping follows. The emission factor of CO2 of crude steel produced from an integrated steel plant route is approximately 3.8 times as high as that produced via an electric are furnace route.