Аннотация:Modelling of microorganism hydrodynamic stress by CFD has been done for stirredtank bioreactor for process of lactic acid production. Maximum dissipation rate has been taken as one of the characteristics of shear stress (as a type of mechanical stress in bioreactor). The zone of high mechanical influence on microorganisms (stress zone) has been defined. It was established the dependencies of stress zone specific volume versus impeller rates in bioreactor for different initial concentrations of substrate that allowed to define the range of recommended impeller rate values.