|The combustion and exhaust emissions characteristics of biodiesel were studied in a single-cylinder diesel engine with about 498 cc of displacement volume under various intake air conditions. Biodiesel used in this work was derived from soybean oil, and it has high viscosity, surface tension, and density compared to a conventional diesel. In addition, biodiesel has an oxygen as 11 %, and it has the influence on the high nitrogen oxides (NOx) and a low soot emission. The single-cylinder diesel engine was operated by AC dynamometer, and its oil temperature and coolant temperature were set to 80 ℃. The emissions, such as NOx, CO, and HC, were measured by the emission analyzer (MEXA-9100DER, Horiba). The test was conducted under 1800 rpm of engine speed, 14 mg of injection quantity, and BTDC 3 º ~BTDC 30 º of injection timings. The temperature of intake air was changed from 30℃ to 60℃. From results, we could analyze the IMEP (indicated mean effective pressure), combustion pressure, emissions (NOx, HC, CO). The increase of intake air temperature induced the increase of NOx and decrease of HC and CO emissions.