Abstract: Theanine is a peculiar amino acid in green tea.It was firstly extracted and refined from tea in 1950’s and its chemical structure was also determined at the same time.Since then many researchers have done a lot of studies on it,including its absorption and metabolism in vivo,detective method,biologicl effects and application to foods.Theanine could be in almost every kind of food,mainly as a food additive.It not only improves the food flavour,but also has health functions,such as reducing blood pressure,relieving fatigue and benefiting clinical chemotherapy.In this paper we summarized the latest research of theanine at home and abroad.

Key words: Theanine , Green tea , Physiological function