In case of cultivation on the ground, the tea is produced about five years after the transplantation. In case of hydroponic cultivation, however, it can start in about two years. Against difficulties due to the high temperature in summer, the cool summer climate of Hokkaido is good for putting the hydroponic cultivation to practical use. As the tea is a nonessential grocery item, its quality is regarded as very important, and determined by its theanine and other free amino acid content. Therefore, a new measurement method by high-speed liquid chromatography was studied to establish the method of quantitatively analyzing the free amino acid. By applying this method established, the hydroponically cultivated tea was qualitatively evaluated through classifying it and measuring its free amino acid content at each of its foliage heights. The main free amino acid contained was known to be theanine, glutamine, arginine, threonine and alamine. The theanine accounted for about 70% of all the free amino acid, and with a decrease in foliage height, its content fell. 15 refs., 20 figs., 2 tabs.