In Korea few previous studies on environmental benefit estimates have been carried out. In particular, no studies have dealt with ancillary benefit of green house gas reduction. In this context ancillary benefit study proposed would (1) play a critical role in cost benefit analysis of climate change by giving a reference of benefit estimates such that it will have a significant impact on climate change policy decision and (2) give a good example on environmental benefit estimation in general and calculation of ancillary benefit in a context of climate change in particular. Recent cost benefit study carried out in Kyonggi Province has revealed a mitigation cost of 3,069 million US dollars and benefit of 743 - 2,069 million dollars associated with mortality and morbidity reduced from PM10, SO2, and O3 over 2000-2007. In developed countries PM is generally regarded as most deleterious pollutant. However, in Korea most epidemiologists have consensus that ozone is the most harmful pollutant. Since, ancillary benefit modeling in Korea is in its fledgling stage, suggestion for the model building is timely and useful. Based on Korean situation of data availability, risk potential, and feasibility, the main frame of future Korean study is recommended to investigate in order of priority PM10, SO2, NO2, and ozone as pollutants and Seoul Metropolitan area, urban area, and nationwide in geographic level to cover.