To provide a method for preparing micropowder obtained by finely pulverizing a solid raw material and placed on the market into readily processable particles having good fluidity for leucine and/or isoleucine.

The method for preparing leucine and/or isoleucine particles is characterized as follows. The micropowder of the leucine and/or isoleucine is molded into a tablet having 100-300 mg weight per tablet and 0.4-1.0 kg hardness by a direct tableting method and micro-vibration is then applied to the resultant tablet on a 20- to a 30-mesh sieve. Thereby, the tablet is roughly pulverized.