This paper reports an experimental study of polystyrene grinding in a shaker bead mill. The objective is to characterize the influence of the operating conditions on the evolution of the particle size. The effects of temperature, vibration frequency, and bead and polymer loads have been examined. Grinding kinetics have been predicted by combinations of four log-normal laws. The number of sub-populations used for the prediction has been defined after SEM observations. The kinetic parameters (mean size, standard deviation and proportionality coefficient) of the different laws have been determined and their evolution during grinding has been analysed.