Not being one of the Parties that ratified the Kyoto Protocol, the greenhouse gas (GHG) emissions estimated in Taiwan ranked 27nd place, contributing about 0.5% to the global total. Sponsored by the R.O.C. EPA, the present research aimed to investigate and quantify the GHG emissions from Environmental Sectors in Taiwan for the years 1990, 1994, and 2000-2004. The defined "Environmental Sectors" consist of landfilling, composting, waste transportation, wastewater treatment, night soil treatment, and solid waste incineration. The preliminary results were compared with that of the United States, Germany, Japan, United Kingdom, and Korea. It was found that only the landfilling and the domestic wastewater treatment are the common sub-sectors that were listed both in the Waste Sector for the UNFCCC and in the Environmental Sector discussed in this study. The GHG national inventory report (NIR) of the five countries from 1997 to 2003 showed that the ratio of the Waste Sector to the total GHG emissions was around 1.67-3.29%, and was gradually declining. The GHG emissions from the Environmental Sectors were mostly estimated by following the default methodology in the IPCC Guidelines, except that of night soil treatment and waste transportation which were modified or newly developed. The GHG emissions from the Environmental Sectors in 2004 were 10,225 Kt CO2 eq. Landfilling (48.86%), solid waste incineration (27%), and wastewater treatment (21.5%) were the major contributors. Methane emission was the most significant GHG (70.6%) followed by carbon dioxide (27.8%) and nitrous oxide (1.6%). In summary, the GHG emissions estimated for the Environmental Sector in Taiwan provided reasonable preliminary results, which were comparable with the other authority data. The recommended mitigation plans include wastewater and solid waste recycling, CH4 recovering for energy, and waste reduction/classification.