Abstract Experimental investigations on the wet batch comminution of an alumina hydrate in a stirred bead mill are presented. The influence of some operating parameters (mass solids concentration, initial size of particles, stirrer speed and beads size) on both the specific energy and the size distribution of the ground product is discussed. The existence of a limit fineness has been put in evidence and the conditions leading to a best efficiency of the process are defined. A quantitative characterization of the morphology of the fragmented particles has led to the identification of the fragmentation path occurring during the process. The analysis allows to interpret the evolution vs. time of the product size distributions characterized by a multimodal pattern.