<p>When the surface clearance is less than 100 times of the thickness (normally on the 1 nm scale) of the adsorbed boundary layer in a hydrodynamic thrust bearing, the effect of the adsorbed boundary layer should be considered. The RMS roughness of the classical bearing surface is normally on the scales of 0.1–1 µm, while that of the micro/nano bearing surface is normally at least on the 1 nm scale. For whichever bearing, when the bearing clearance is so low that the effect of the adsorbed boundary layer should be considered, the effect of the surface roughness of the bearing should also be considered. The present paper presents the multiscale calculation results for the surface roughness effect in the hydrodynamic wedge-platform thrust bearing with small surface clearances. It was found that in the studied model of the bearing the hydrodynamic pressure as well as the carried load of the bearing are significantly increased with the increase of the surface roughness; this is due to the effect of the adsorbed boundary layer. The findings is new and has an important implication to the modeling of mixed lubrication with small surface clearances.</p>