Biomass co-combustion to pulverized coal power plants has been widely used in many countries, but there have been arguments on its effect to emission of fine particulate matter(PM) with regard to aerosol formation caused by alkali compounds such as potassium during biomass co-combustion. This study is aimed to experimentally investigate the effect through an 80 kWth-scale pulverized coal combustion system. Thermal input of 30% was replaced with wood pellets and combusted in the experiment, and concentrations of particulate matter in the combustion gas were measured with varying gas temperatures. Particle size distribution from 0.1 to 60 ㎛ was measured as well and the results were compared with a case of 100% coal combustion. In the result, generation of particulate matter in case of the wood pellet co-combustion was significantly decreased for all gas temperatures and all particle sizes, compared with 100% coal combustion case. It shows that lower ash content in the wood pellets gave more impact to the less PM generation, even though the wood pellet contained higher potassium than coal.