--------------------------------------------------------------------------------------------------------------------------------Abstract Diesel-biodiesel blends improve the performance and reduce the emission effects in a compression ignition engine except Nox. Cetane improves reduce the ignition delay, which in turn reduces the combustion temperatures thereby reduces Nox emissions. The present work was aimed at an experimental investigation of Ethanol (ETN) as an additive to the diesel-biodiesel blends. Experiments were conducted on a 4-stroke single cylinder diesel engine by varying the percentage by volume of ETN in diesel-biodiesel blends. The effect of ETN on Brake Thermal Efficiency (BTE), Brake Specific Fuel Consumption (BSFC), cylinder pressure and exhaust emissions was studied. It is found that cylinder pressure was lower at higher ETN percentage which was accompanied by an increase in BTE and smoke density. Further CO and Nox emissions were reduced with increase in ETN percentage.