This research evaluated the amount of greenhouse gas (GHGs) emissions from wastewater of the central wastewater treatment system at Mahidol University, Salaya campus, during the in years 2009-2012 by comparing two treatment systems: an oxidation pond and an extended aeration activated sludge. Researchers used the equation from the guidelines of the clean development mechanism (CDM) compares with the equation from carbon footprint for organizations (CPO).