The transient grating method is used for investigating the diffusion dynamics of the transient radicals created by photoinduced hydrogen abstraction reactions of benzophenone (BP) in various solvents, acetone in 2-propanol, and acetoaldehyde in ethanol. The diffusion coefficients (D) of the BP kethyl radical and BP are obtained simultaneously. In acetone/2-propanol and acetoaldehyde/ethanol systems, only the signals due to intermediate radicals are observed. The D values of the transient radicals are two to three times smaller than those of BP. The measured Ds of the radicals usually show good agreement with the theoretically calculated values on the basis of the Stokes-Einstein (SE) relationship, whereas the SE relation underestimates D for stable parent molecules and the values are reproduced by the modified SE equation by Spernol and Wirtz. The smaller D values suggest the existence of a specific radical-molecule interaction.