Microsized-air bubbles (MB) have been regarded as a promising additive for fuels in internal combustion engines. In this study, the effects of MB-mixed fuels on performance and emission were investigated in a single-cylinder four-stroke diesel engine under varying engine speeds. The MB were generated via the hydraulic cavitation method using a venturi nozzle in the diesel fuel (D100) and diesel-biodiesel blend (B10). In the presence of MB, the results showed a decrease in the density and calorific value by up to 0.013 and 0.123%, respectively, and an increase in the viscosity (up to 0.025%) for both types of fuels. In terms of performance, the MB-mixed B10 fuel improved the brake thermal efficiency (BTE) by an average of 1.5% and reduced the brake specific energy consumption (BSEC) by 1.4%. In terms of emission, an increment in CO2 and NOx emissions was observed when MB were incorporated in both fuel types. In conclusion, it was found that an engine fueled with MB-mixed B10 yielded better efficiency in terms of performance and emission in comparison to MB-mixed D100. With many benefits such as easy to produce and low cost, MB hold great potential as a fuel additive.