Biodiesel productions from Mahua oil using two different catalysts, including KOH and activated red mud by catalytic cracking (waste from aluminum industry) were compared in distinctive blends of diesel fuel. Red mud was subjected to characterization studies to find the mechanism of red mud during catalytic cracking using Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscope (SEM). The cracking process was carried at 300 degrees C for 2 h and different blends of biodiesel (B25, B50, B75, and B100) were examined for physical properties. Furthermore, the different blends were subjected to a four-stroke diesel engine to study its engine performance. The results showed that the changes in elemental composition during EDS analysis could be an important reason for red mud to have a better calorific value (10,601 kcal/kg) compared to KOH as a catalyst The NOx emission from KOH biodiesel was 7.5% higher compared to red mud biodiesel when it was blended 100% at 1500 RPM at a maximum brake power (52 kW). From the findings of this study, it was evident that using red mud as a catalyst not just increases most of the properties of the fuel, but also reduces the stress on the environment in the form of less emission and fuel consumption. Since red mud was a hazardous waste from aluminum industry, utilizing it for biodiesel productions could also be an economically viable option. (C) 2016 Elsevier B.V. All rights reserved.