Abstract: Objective To study the effect of theanine on the fatigue.Methods After the mice were administered for 30 days,the swimming test were carried out,and the death time was observed and recorded;after mice swimmed for a period,the blood were taken for determinig urea nitrogen in serum and lactic acid in blood;The liver were taken for determinig the glycogen.Results Theanine prolonged significanty the time of mice swimming,decreased the consumption of glycogen and the level of urea nitrogen in serum;Also theanine inhibited the augment of lactic acid in blood caused by swimming,and accelerated the elimination of the increased lactive acid in blood.Conclusion Theanine could have the action of anti-fatigue.