This research describes the working behaviours of the Compression Ignition (CI) engine using Mahua Pyrolysis Oil (MPO) obtained from Mahua seed using the fast pyrolysis technique. The diesel engine test was performed with four different MPO-diesel mixtures such as MPO15, MPO25, MPO35 and MPO50 and the test results were compared to diesel engine. According to the results of the tests, the Brake Thermal Efficiency (BTE) in MPO-diesel mixture was decreased by 2-5% with an increase in the Brake Specific Fuel Consumption (BSFC) compared to diesel. Higher Carbon Monoxide (CO) and Hydrocarbon (HC) emissions were observed when the mixture’s ratios increased. At maximum power, Nitrogen Oxide (NO) and smoke were diminished by 9% and 17% for the MPO25-diesel mix. Results also revealed that the combustion parameters like cylinder peak pressure and the Heat Release Rate (HRR) were increased in an increased blend. The results suggest that up to 25% of the MPO mixture is the optimum fuel for running the engine without much affecting the performance and emissions. © 2023 Elsevier B.V., All rights reserved.