We study the effects of the solvation structure on the diffusion of a large particle in a binary mixture. Using our recently developed perturbation theory, we calculate the diffusion coefficient of a large hard-sphere solute particle immersed in a binary solvent mixture of hard spheres with two different sizes. The calculation results show that the Stokes-Einstein (SE) relation breaks down in the hard-sphere system. When the size ratio of binary solvent spheres is three or more, the deviation from the SE relation increases with the packing fraction of larger solvent spheres. In contrast, at the size ratio of two, the diffusion coefficient approaches the value predicted by the SE relation as larger solvent spheres are added. We show that the large deviation from the SE relation is caused by the high density of larger solvent spheres around the solute sphere. (C) 2014 Elsevier B.V. All rights reserved.