The potential mitigation of greenhouse gas (GHG) is studied in the Pohang steel industrial complex (PHSIC). The total GHG emission in 2010 is estimated to be in the range from 4,174,000 to 4,574,000 tCO2-eq in PHSIC. To meet the target proposed by the government, it is needed to reduce 552,000 tCO2-eq at minium by 2020. To estimate the potential amount of GHG reduction, the technologies used in the voluntary carbon reduction projects are applied to 51 companies which are subject to GHG target management. From the viewpoint of technological availability and payback period, the fuel conversion and waste heat recovery have an advantage in the short term with a possibility to reduce 160,000 tCO2-eq. In the mid term, the thermal technologies in steel and iron industry have the potential to cut 229,000 tCO2-eq, while the electrical technologies have the potential of 125,000 tCO2-eq reduction. The gap between the target GHG mitigation and potential reduction using the short and mid term technologies is about 38,000 tCO2-eq, which should be compensated by the fundamental process innovation and the implementation of the most cutting-edge technologies including renewable energy.