Bioenergy crop production is an alternative management practice that has the potential to help mitigate the greenhouse effect. Estimates of greenhouse gas (GHG) emissions and SOC sequestration associated with their production are needed to determine their benefit. A field experiment was established in 2004 in Urbana IL to investigate GHG and SOC sequestration in the fields planted with Miscanthus (Miscanthus x gigantus) and switchgrass (Panicum virgantum). During the establishment phase (second year after planting), the primary data on the emission rates of N2O and CO2, soil temperature, soil water content, bulk density, and available N contents was measured every two weeks from May to October, 2005. Total and particulate organic matter (POM) C and N contents were measured for samples collected in spring 2005 and the data was compared with total and POM C and N contents determined for soil samples taken from adjacent 1 yr and 4 yr old stands of bioenergy crops. The global warming potentials of establishment phase and mature bioenergy crop fields and of fields in corn/soybean production were calculated using the denitrification-decomposition (DNDC) model. The SOC sequestration was not enhanced after 1 year of bioenergy crop production but had increased in the 4 yr old stands; where, sequestration rates were 0.30 t/ha/yr for Miscanthus, and 0.19 t/ha/yr for switchgrass, respectively. Preliminary data on the annual global warming potentials of will be discussed.