AISI 4140 steel is a popular low alloy steel due to its wide applications as workpiece in the metal-mechanic industry; there are extensive research about surface modification to enhance its properties for specific applications. The focus of this study was to investigate the influence of the nature of lubricants, mineral and vegetable oils, on the tribological performance of the hardened and tempered AISI 4140 steel against alumina (Al2O3). For this purpose, friction tests were conducted in a pin on disc tribometer according to ASTM standard G 99-05, at room temperature of 25 °C and in air with about 30% relative humidity. Lubricants were selected to be commercial Holifa B22/2 oil as mineral oil and Castor Oil as bio-lubricant, with kinematic viscosity at 25 °C of 667 and 662 cSt respectively. The following conditions were settled for all the experiments: relative sliding speed of 0.05 ms-1, sliding distance of 1000 m and wear track radius of 2 mm. Friction behaviour was reported as the average kinetic friction coefficient (µK) while wear performance was evaluated as wear rate (K). In order to identify and determine wear mechanisms, worn surfaces were analyzed by optical microscopy and profilometry. It was found that, for these tribosystems, hardened and tempered AISI 4140 steel had the best friction and wear performance under lubrication with Castor Oil. The lowest µK achieved was 0.035, whereas the lowest K was 1.02x10-8 mm3/Nm. With this bio-lubricant, there were reductions in friction and wear up to 72% compared with those under mineral oil lubrication.