The aim of this paper was to explore the preparation method of two-dimensional MoS2 nanosheets with ultra-thin structure and their friction-reducing and anti-wear properties in engine oils. In this paper, two-dimensional MoS2 nanosheets with surface modified by oleylamine molecules were prepared by in-situ surface method using ammonium heptamolybdate and thiourea as reaction precursors and oleylamine as the reaction solvent. The morphology, surface state, and chemical composition of the prepared MoS2 nanosheets were characterized by transmission electron microscopy (TEM), infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS), respectively. Further, the tribological property of the fabricated two-dimensional nanosheet MoS2 as lubricating additives in engine oils was tested on a ball-on-disk tribometer, and the wear scars were analyzed by a white-light interference profilometer, scanning electron microscope (SEM) and XPS. Results showed that the prepared two- dimensional MoS2 nanosheets with ultra-thin structure has good anti-friction and anti-wear properties in engine oils. The friction coefficient was decreased by 27.1% and the wear scar diameter was reduced by 17.17% after adding 3wt% two-dimensional MoS2 nanosheets into oils. It was worth pointing out that at the high temperature of 150 ℃, the friction coefficient suddenly increased to 0.5 at the initial stage of friction, and lubrication failure occurred when the pure engine oil was used for lubrication. However, for the case lubricated with two-dimensional MoS2 nanosheets, the friction coefficient was relatively stable during the whole friction process at the high temperature of 150 ℃. In addition, the wear volume and maximum wear scar depth were only 23.44 % and 28.53% of these lubricated with the pure engine oil, respectively, at the high temperature of 150 ℃. During the friction test, the two friction surfaces were in the boundary lubrication region, and the two-dimensional MoS2 nanosheets with ultra-thin structure entered the friction contact area with lubricating oil, which exerted a good lubrication effect. Especially, when the lubrication of the pure engine oil failed at high temperature, the two-dimensional MoS2 nanosheets could form MoS2-based tribochemical reaction film on rubbing surfaces that filled and repaired the worn surfaces, which acted the lubrication effect.