The kinetics of the dissolution Of L-aspartic acid crystals under the gentle and vigorous agitation was investigated. A dissolution rate equation was derived by assuming two steps: the disintegration of molecules from the surface of crystals and the mass transfer of disintegrated molecules into the bulk solution. An intrinsic expression of the relationship between the solute concentration of the bulk solution and the dissolution time was also derived. The dissolution process of monodisperse and polydisperse crystals Of L-aspartic acid was well estimated, and the change of crystal size distribution of polydisperse crystals during dissolution was simulated with good accuracy.