To elucidate the characteristics of fine particulate matter pollutant emitted from a diesel engine, a fossil-based diesel fuel (D100) and two blended fuels consisting of D100 and waste cooking oil (WCO) convered biodiesel (W) are tested with a diesel engine generator at loads of 1.5 kW and 3.0 kW. The blended fuels contain 20% and 40% W and are referred to as W20 and W40, respectively. The PM2.5 emissions and their polycyclic aromatic hydrocarbon (PAH) and metallic components are investigated. Experimental results show that higher concentrations of PM2.5, PM2.5-bound ΣPAHs and Σmetals, and ΣBaPeq are generated at the 3.0 kW load, with its greater fuel consumption (FC), than the 1.5 kW load. Additionally, of the three fuels, using W20 emits the lowest concentrations of PM2.5, PM2.5-bound ΣPAHs, and ΣBaPeq. Specifically, the reduction in ΣBaPeq mainly results from the effective inhibition of HMW-BaPeq. Conversely, when using W40, the PM2.5-bound Σmetals significantly decreases, and its composition is strongly affected by the metallic content in the fuel. Although W20 and W40 exhibit higher FC (3.0% more) and brake-specific fuel consumption (BSFC; 3.1% more) than D100, they generate lower concentrations of PM2.5 (18.1% less), PM2.5-bound ΣPAHs (22.8% less) and Σmetals (22.0% less), and ΣBaPeq (35.0% less) at both engine loads. The emission factors of these pollutants in the engine exhaust are also reduced , particularly at the higher load (3.0 kW). Accordingly, WCO-based biodiesel additives may decrease the PM2.5, PAHs, and metals exhausted by diesel engines, thus reducing the BaPeq of these emissions.