This research analyzes the impact of biomass co-firing on CO2 emissions and electricity production in coal-fired power plants (PLTU) Punagaya. The background of this study is that the energy sector serves as the backbone of economic development, including in Indonesia, where energy demand continues to rise alongside economic growth. However, in Indonesia, coal-fired power plants (PLTU) still dominate the national electricity system, with a high dependency on coal. According to data from the Ministry of Energy and Mineral Resources (ESDM), approximately 50% of power generation in Indonesia is coal-based. Meanwhile, coal consumption causes pollution, while the use of renewable energy can reduce emissions. This study discusses how co-firing can optimize emissions and increase electricity production in PLTU. The problem formulation focuses on the impact of biomass addition on CO2 emission levels and electricity production in PLTU. The objective of this research is to analyze the effect of biomass addition in the co-firing process on CO2 emission levels in PLTU and to analyze the effect of biomass addition in the co-firing process on electricity production in PLTU. The research method involves literature studies and interviews, with data analysis using formulas based on Tier 1 of the Intergovernmental Panel on Climate Change (IPCC) 2006. The results show that biomass co-firing does not increase total CO2 emissions. For Unit 1, CO2 emissions remain at 808,365.81 tons CO2, whether using pure coal or a biomass blend. A similar pattern occurs in Unit 2, with emissions at 698,328.78 tons CO2. This is because biomass is considered carbon neutral, and the amount of coal burned does not increase. Conversely, electricity production significantly increases. Unit 1 generates 728,178.53 MWh with the biomass blend, higher than the 649,215.66 MWh from pure coal. Unit 2 also shows an increase from 558,175.32 MWh to 624,983.23 MWh.