The purpose of this study is to establish a method for evaluation of the strength of fragile granules such as ferric oxide granules produced by spray pyrolysis from an acid solution of a metallic salt. To examine if they have enough strength to maintain their shape throughout the handling process, and at the same time, enough weakness to break down easily during a specifically designated processing. An attrition test using a Ro-Tap sieve shaker, which is usually used for particle size analysis, was employed. An attrition rate equation was derived from the attrition mechanism of granules on a sieve; a method for the evaluation of strength based on the attrition equation is presented.