Abstract: An artificial complex of amino acids (C Ⅰ)was made by mixing 18 synthetic amino acids, according to the kinds and contents the amino acid contained in the natural Cordyceps sinensis Sacc., It showed the same sedative action as the natural C. sinensis, as indicated by the spontaneous activity inhibition in mice (photocell method ).However, the action of commercial complex amino acid injection(12 X, total amino acid components are similar to C Ⅰ )was more attenuated than that of C Ⅰ. Comparing amino acid components of 12 X with C Ⅰ, the latter was found to contain 5 times as much glutamic acid, tryptophan and tyrosine as those of 12 X (tab 1). Another artificial amino acid complex (C Ⅱ) consisting of the above mentioned 3 amino acids, also showed the same sedative action. This suggests that tryptophan is the principal component by orthogonal test .However ,C Ⅱ did not enhance the phagocytic action of mononucleophagocyte as the natural C. Sinensis did in the clear rate test of carbon granule from mice serum.