The castor oil was characterized using Infrared spectrometer and its tribological properties as antiwear additive in jet fuel were evaluated using the High Frequency reciprocating rig (HFRR).The morphologies and elemental distributions of the worn steel surface lubricated by castor oil were analyzed by means of scanning electron microscopy and EDS for discussing its lubricating mechanism.The results show that the jet fuel shows a good sensitivity to castor oil, and castor acid contributes to improve the lubricity of jet fuel.The antiwear mechanism of castor oil can be concluded that castor acid is adsorbed on the metal surface physically at first, while a chemicaladsorbing film of containing oxygen is formed at a mass addition of castor oil, resulting in a good lubricating effect.