Abstract: Changes in the molecular mobility of hen egg white lysome(HEWL)in aqueous solution and in agarose gel were measured by pulsed-field-gradient stimulated echo (PFG-STE) ¹H NMR and spin-spin relaxation time(T₂) ¹H NMR methods in order to elucidate the effect of agarose gel on the crystallization of protein. Both the diffusion coefficient of HEWL(D_HEWL) and T₂ of HEWL showed a steep decrease with the increase of agarose concentration. These results suggested that both the local molecular motion and translational molecular motion were impeded by the three-dimensional polymeric network of agarose gel, with the result of a higher local concentration of HEWL in agarose gel. The low diffusion of HEWL molecules in agarose gel probably retained the higher local concentration for a longer time, which enhanced the nucleation. In addition, in the supersaturated solution, HEWL clusters diffused more slowly than monomers due to the large hydrodynamic interaction with the agarose matrix and their small hydrodynamic radius, which promoted the crystallization of the HEWL protein.