Auto-ignition behavior of lubricating oil is studied experimentally using a cone calorimeter. Based on its Material Safety Data Sheet (MSDS), the adopted lubricating oil has a flash point temperature of 228°C, The measurement of auto-ignition behavior was carried at atmospheric pressure in range of temperature between 350°C to 550°C. In this work, the optical density of smoke resulting from the combustion process was measured at auto-ignition temperature. The result of this study shows that the auto-ignition behavior of lubricating oil is strongly depend on conditions of gas mixture, i.e. oil vapor, nitrogen, and oxygen mixtures. The lubricating oil started to ignite at irradiance temperature of cone heater at 500°C with a measured heat flux value of 16,7 kW/m2. At lower temperatures ignition of the mixture occured by piloted igniton sources. No ignition was observed at temperature less than 350°C. At higher irradiance temperature and heat flux (550°C and 21,1 kW/m2), auto-ignition occured at shorter time to ignition and producing higher value of smoke's optical density of 1 - 1.4 m-1.