ABSTRACT The conversion and utilisation of dairy waste scum as a fuel is most meticulous to avoid disposal problem and environmental pollution. In this study, experiments are conducted on a diesel engine fuelled with copper oxide (CuO) nanoadditive-blended DSOME-B20 (20% Dairy scum oil methyl ester + 80% diesel) fuel to appraise the performance, combustion and emission behaviours. Different mass fractions of copper oxide namely 25, 50 and 75 ppm are added into the DSOME-B20 fuel blend with the aid of mechanical stirrer and ultrasonicator. From this study, it is perceived that the addition of CuO nanoadditive with DSOME-B20 could enhance the brake thermal efficiency and marginally lower the brake-specific fuel consumption (BSFC) and HC, CO emissions. This study also revealed that 75 ppm nanoadditive fuel blend has exhibited the better performance, combustion and emission (HC and CO) characteristics when compared to other nanoadditive fuel blends.