. The utilization of co-firing (coal-biomass) in shamrock xisting coal-fired power plants (CFPPs) is the fastest and most effective way to increase the renewable energy mix, which has been dominated by pulverized coal (PC) boilers, particularly in the Indonesian context. This study aims to investigate the technical and economic aspects of co-firing by conducting a pilot project of three PC boiler plants and capturing several preliminary figures before being implemented for the entire plants in Indonesia. Various measured variables, such as plant efficiency, furnace exit gas temperature (FECT), fuel characteristic, generating cost (GC), and flue gas emissions, were identified and compared between coal-firing and 56-biomass co-firing. The result from three different capacities of CFPT shows that co-ring impacts the efficiency of the plant corresponding to biomass heating value linearly and has an insignificant impact on FECT. Regarding environmental impact, co-liring has a high potential to reduce SO, and NO. emission depending on the sulfur and nitrogen content of biomass. 50 emission decreases by a maximum of 34% and a minimum of 1.00%. While according to economic evaluation, the average electricity GC increases by abod 0.25 USD cent/kWh due to biomes price per unit of energy is higher than coal by 0.64x10 degrees *USD cent/cal. The accumulation in the one-year operation of 5%-biomas co-firing with a 70% capacity factor produced 205,676 MWh of green ergy, equal to 323,749 CO2 and 143,474 USD of cabo credit. The biomas prices mitivity analysis found that the fuel price per unit of energy between biomass and coal was the significant parameter to the GC changes.