The diesel fuel was mixed with the rice husk bio-oil using some emulsifiers based on the theory of Hydrophile-Lipophile Balance (HLB). The lubricity of the bio-oil/diesel fuel blend was studied on a High Frequency Reciprocating Test Rig (HFRR) according to ASTM D 6079-2004. The microscopic topography and chemical composition on the worn surface were analyzed respectively using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The profile and surface roughness of the rubbed trace were measured using a profilometer. The chemical group and composition were studied by a Fourier transform infrared spectrometry (FTIR). The results showed that the lubrication ability of the present fuel blend was better than that of the Chinese conventional diesel fuel (number zero). However, the anti-corrosion and anti-wear properties of the fuel blend were not satisfactory in comparison with those of conventional diesel fuel. (C) 2009 Elsevier Ltd. All rights reserved.