A method of ultrafinely pulverizing oat bran and a beverage composition containing an effective oat bran component prepared using the method are provided. The method includes primarily pulverizing oat bran, and jetting the primarily pulverized oat bran powder at a high rate to collide against a freeze wall. The effective oat bran component in the beverage composition is extracted by adding warm water to ultrafinely pulverized oat bran powder obtained using the method and stirring the mixture.