Recently, hazardous properties of synthetic substances contained in foods and medicines have been observed. Therefore, the pharmacological actions of natural substances became the focus of attention. Catechins, which are polyphenols, are abundant in green tea. To extract green tea catechins, there are two types of method: extraction using hot water and organic solvents. In the extraction using hot water, green tea quality deteriorates and catechins are destroyed due to the heat applied. Accordingly, the extraction of catechins at low temperatures is appropriate, although the efficiency is low. Therefore, we attempted to increase the amount of catechins extracted with ultrasonic irradiation.