Wear of glass beads used in an agitation bead mill as grinding media was observed in detail with varying amount and hardness of the powders to be ground. Wear and surface damage of the beads were examined by a weight loss during grinding, scanning electron microscopic observation, and three-dimensional profilograms of the bead surface before and after etching by an aqueous solution of potassium hydroxide. The amount of weight loss and the feature of surface damage varied significantly with the material to be ground, even under the same operating condition of the mill. Observed microcracks after etching revealed the difference in the loading conditions during collision or compression of two beads and subsequent microcrack initiation depending on the hardness of the powders to be ground.