Vegetable oils due to high biodegradability, low toxicity, renewability and excellent lubricating performance, have immense potential to replace mineral oils as feedstock for lubricants. Owing to these aspects environmentalists and engineers have made attempts to explore the possibilities of using vegetable oils as environmentally friendly lubricants for range of applications. In this work, the tribological properties of castor oil and sesame oil in the presence of 12-hydroxystearic acid as anti-wear additive were investigated using four-ball tribometer. The viscosity, acid value, peroxide value and iodine value of the selected oils were determined experimentally following AOCS methods. Results revealed that the addition of 12-hydroxystearic acid improved the anti-wear performance of the selected vegetable oils. Moreover, it was noted from the results that 12-hydroxystearic acid was more effective as anti-wear additive in the castor oil as compared to sesame oil under similar experimental conditions. The improved anti-wear performance of the selected vegetable oils in the presence of additive may be attributed to the formation of protective layer as a result of tribochemical reaction on the metal surface. © 2011 Asian Network for Scientific Information.