Tea is the most widely consumed drink in the world and consists of three major types: green tea, oolong tea, and black tea. Tea contains a variety of natural medicines and these chemical metabolites are known to exhibits various biological activities. The composition of the tea metabolites depends on several factors including genetic strain, climatic conditions, soil, growth altitude, and the plucking season of leaves. Green tea, which is manly consumed in Asia and Northern Africa, contains a great amount of natural medicines such as tea polyphenols, caffeine, theanine, and vitamins. The plucking season of leaves is one of the important parameters that influence the metabolic diversity of green tea. Green tea is classified as several grades which depend on the plucking timing of leaves in Korea: “Ujeon” (plucked before 20th, April), “Sejak” (plucked in late April or early May), “Jungjak” (plucked in the middle of May), and “Daejak” (plucked in late May or early June). Generally, as the leaves are plucked earlier, the flavour and aroma of green tea are thought to be better and then the grade of green tea becomes higher. Hadong county is one of three famous area for green tea in Korea (the other two areas are Boseong and Jeju). In order to understand the correlation between the metabolite contents and quality of the Hadong green teas, we have performed NMR experiments on the extract of three classes of the Hadong green tea. The metabolite profiling results provide the information required for quality control of the green tea products. In addition, this NMR study also shows the important chemical compounds of the green teas which are strongly correlated to the harvest timing of leaves and the grade (including flavour and aroma) of green teas.