Forest biomass has always played an important role in the Brazilian energy mix, with eucalyptus presenting high levels of production and productivity. Due to the high expected potential of this woody biomass, this study assesses this resource for thermal energy production, contributing to the expansion of this sector and to energy transition strategies. This study developed a Life Cycle Assessment (LCA) to quantify the environmental impacts associated with the combustion of eucalyptus. LCA data, which included the procurement of eucalyptus and wood ash treatment, was implemented in exergy and exergoenvironmental analyses, based on the SPecific Exergy COsting (SPECO) approach, for a steam power plant fueled by eucalyptus biomass. Fuel combustion takes into account the formation of pollutants. The high moisture content of biomass affects the overall and boiler exergy efficiencies. The components with worse environmental performance are those with high environmental impact rates associated with exergy destruction (feed water and pump). The environmental impact rate per exergy unit of electricity is 7715 mPt/GJ. A sensitivity analysis verifies the effect of biomass moisture on boiler efficiency and on the specific environmental impact associated with power, concluding that an increase in boiler efficiency increases global efficiency and decreases the specific environmental impact, resulting in a reduction of global exergy destruction