We investigate the effect of roughness degree of a protein surface on the solvent diffusion near the surface by carrying out the molecular dynamics simulations. As expected, the solvent molecules experience the larger frictional drag on a more corrugated protein surface. However, the roughness degree of a protein surface can be measured differently by different solvent molecules. It is shown that on the same protein surface the smaller solvent molecules experience the larger frictional drag than the larger ones. The observed trends in the mobility of solvent molecules on the protein surface correlates nicely with the correlation dimension of the protein surface, which we proposed recently as a new measure of the molecular surface roughness.