To control an adequate size of aggregate in suspension cell culture is an essential factor for facilitating the cell growth and enhancing the secondary metabolite(s). The effect of hydrodynamic shear stress on aggregate size of plant cell in suspension culture was investigated. Kinetic equations regarding the growth rate of cells within an aggregate were proposed. A parameter, aggregate disruption rate constant, beta in the proposed model implied that the aggregate disruption was caused by hydrodynamic shear. Equations relating the Kolmogoroffs eddy size, energy dissipation and beta in a turbulent flow region were obtained by referring to the turbulent theory. The aggregate size was affected remarkably by beta and eddy size. beta is affected by apparent viscosity of culture broth and energy dissipation of the culture medium. The time course changes of aggregate size in the shake flask and stirred bioreactor were consistent with calculated data of proposed equations, ＇The proposed kinetic model enables one to simulate the experimental results of plant cell aggregate changes in shake flask and stirred bioreactor cultures successfully. The proposed model is thought to be a guideline for hydrodynamic controlling of aggregate size in plant cell culture system.