because of it beneficial health effects, more data on the catechin content of green tea are needed. The level of catechins in commercial Thai green teas has not been determined yet. Thus, this study aimed to determine the main quality indicatos and the eight kinds of catechins in green tea produced in Chiang Rai, Thailand. In addition, the level of catechins determined in this study can be a new potentially useful indicator for assessing the quality of green teas in Thailand. The chemical structure of the common catechins is shown in Figure 1.