This study investigates the performance of a Diesel Oxidation Catalyst (DOC) when transitioning from conventional diesel (B7) to 100% biodiesel (B100), with a focus on emissions reduction in compliance with stringent environmental regulations. Our experiments reveal that B100 achieves a lower light-off temperature and demonstrates superior hydrocarbon (HC) storage capacity compared to diesel, indicating enhanced initial emission control. However, B100's lower energy density results in increased brake-specific fuel consumption (BSFC) and elevated nitrogen oxide (NOx) emissions. The study also highlights biodiesel's advantages in reducing raw soot emissions and its comparable performance to diesel in aftertreatment system (ATS) efficiency. Nonetheless, challenges arise from biodiesel's higher HC slip and distinct combustion properties, necessitating tailored DOC strategies for optimal performance. These findings provide valuable insights for optimizing aftertreatment systems as the transportation sector transitions to renewable fuel sources.