The results of modelling the effect of cell sizes on the microorganism disintegration process are presented. Experiments were conducted in a horizontal bead mill for baker's yeast Saccharomyces cerevisiae. The kinetics of the cell disruption process was investigated by optical image analysis and the release of intracellular protein by Bradford method. A large variation in the size of yeast from one production cyde has been demonstrated. A significant increase in the constant rate of the process with an increase in the range of the cell size class was demonstrated. More beneficial values of the coefficient of determination were obtained for the spherical model of the cell. Worse results of the process description were obtained for the ellipsoidal model. They may result from large variations in cell volume in individual size classes. The greatest changes in the cell Elongation parameter within one size class ranged from 1.00 to 1.54. (C) 2020 The Authors. Published by Elsevier B.V.