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Reducing the coefficient of boundary friction on steel surfaces is one of key technologies to improve the efficiency of machines such as automotive engines. It has been shown that the boundary friction on nanostructured steel surfaces in the sliding test using hydrocarbon lubricant molecules is smaller than the friction of normal steel surfaces. The main difference between the nanostructured and a normal surfaces is the density of grain boundaries and other surface defects. The surface defect can attract lubricant molecules and enhance lubricating film formation on metal surfaces. This can be one of the mechanisms that induce the friction reduction on the nanosructured steel surface. In this work, using first principles calculations, the adsorbability of a lubricant molecule, a fatty acid, on a defected iron surfaces has been studied. Adsorbability of the Fe(110) surface with symmetrical tilt ��3(111) grain boundary was compared to that of the clean Fe(110) surface. As a result, we found that the molecule is adsorbed on sites close to the grain boundary more strongly (0.77 eV in average) than on the Fe surface without grain boundary., 11 pages, 6 figures