CO2 emission from biomass power generation system with sustain-able afforestation was evaluated by LCA (Life Cycle Assessment) methodology. Cal-culation was conducted for typical case (15km×15km). CO2 emission from sustainable afforestation system was calculated to be 2.1×107 kg-CO2/y. That from construction of biomass power plants was calculated to be 5.0×105 kg-CO2/y. CO2 emission from power plant construction was negligibly small. Net CO2 reduction effect of replacing coal by biomass was calculated to be 2.4×108 kg-CO2/y. It was suggested that the biomass power generation system possibly educes large quantity of CO2 emission by the replacement. CO2 emission from afforestation was about 8% of the CO2 reduction effect. Finally, the energy payback time of the biomass power generation system with sustain-able afforestation was calculated to be about 0.2 year.
