The body fat reducing effect of tea catechins was previously confirmed in humans. The effects of tea catechins for reducing body fat were thus studied as basis for actual application. Three experiments on healthy male adults (n = 82) were conducted to determine the effects of long-term tea catechins administration on body fat and biochemical blood parameters. First experiment: tea catechins were given as oolong tea-like beverage for 12 weeks. In 600 and 900 mg groups, visceral fat was significantly loss than in the control (600 mg group p = 0.0317, 900 mg group p = 0.0098). The effects were more pronounced at greater of tea catechins administration. No significant changes in biochemical blood parameters including fat-soluble vitamins were detected. Second experiment: oolong tea-like beverage containing tea catechins at nearly same amounts on in the 600 mg group was given for 20 weeks. Abdominal fat, including visceral fat, was significantly loss than in the control (total fat area p < 0.0001, visceral fat area p = 0.0004, subcutaneous fat area p = 0.0001). Plasma PAI-1 was also significantly decreased (p = 0.0080). Third experiment: green tea-like (GT group) and oolong tea-like (OT group) beverages containing approximately 540 mg tea catechins were given for 12 weeks. In the two groups, visceral fat was significantly loss than in the control (GT group p = 0.0284, OT group p = 0.0095) and the effects of two beverages were similar. Long-term tea catechins administration at 500 to 600 mg/day in humans would thus appear to reduce body fat without influencing fat-soluble vitamins, of which the absorption may be inhibited, and various serum and plasma indices regardless of the kind of beverages.