High concentration of carbon dioxide (CO2) is known as a major factor of global warming. In 2008, China is the first rank as the country with the most amount of CO2 released to the atmosphere which led China to maximize the consumption of clean energy in terms of biomass fuels and biomass pellets to replace the fossil fuel. Pellet fuels are widely consumed in Europe and North America since 2005 while China starts to consume this fuel in 2008 and increase rapidly to 2 million tons in 2010. However, a few studies exist to evaluate the consequences of consuming this fuels. The objectives of this research are to determine and compare the emission factor(EFs) of CO2 and CO from uncompressed biomass and pellet under real residential application and to investigate the influences of fuel properties and combustion conditions of CO2 and CO emissions.