Stirring operations in a crystallizer often induce particle abrasion caused by particle-impeller collision, resulting in numerous attrition fragments. This study developed a method for measuring the size and total number of attrition crystal fragments in a stirred vessel filled with anti-solvent, using potassium alum as the model crystal based on image-processing algorithms of SEM images ot attrition fragments. The abraded volume ratio of a parent crystal was also evaluated, based on the edge length of the regular octahedron of a single potassium alum crystal. Results showed that both the number of attrition fragments and the abraded volume of parent crystals initially increased rapidly and reached saturation after about 40 h. The conical parent crystal became rounded with stirring time, although its flat surfaces did not change to any great degree. The rate of attrition fragment generation, which is correlated with the abraded ratio of the parent crystal, decreased rapidly to a few tenths as the parent crystal became rounded.