A comparative study of combustion characteristics and brake thermal efficiency of a diesel engine fueled with diesel and biodiesel (FAME100%) at high altitude (4500 m) were conducted. A 6.7 L heavy-duty turbocharged, common-rail diesel engine meeting EURO III standard was employed. In this present paper, tests were carried out on an on-board engine bench system in high altitude regions instead of simulating devices in laboratories. Two operating conditions were selected to reflect the engine performance in low-speed high-load and high-speed high-load conditions. Calibration of the engine was kept unchanged when the test engine was fueled with diesel and biodiesel respectively. Experiment results revealed that the peak heat release rate of biodiesel operations in premixed combustion duration was a little earlier but lower than that of diesel operations. The start of combustion and combustion duration for diesel and biodiesel operations were very similar. CA50 for biodiesel was 0.4 degrees CA postponed in both operating conditions. By fuelling with biodiesel, there was a decrease of about 0.6% in BTE of the engine. Meanwhile, increases of approximately 2%, 17% and 11% in BSEC, BSFC and volumetric BSFC were observed. Comparison of exhaust mass flow inferred that biodiesel fuelling was helpful to reduce the fresh air consumption when the engine was operating at high altitude. (c) 2013 Elsevier Ltd. All rights reserved.