Abstract: By use of octadecyl (C18) column made in China, a RP HPLC method was studied using phenylisothiocyanate (PITC) as the pre column derivatizing reagent for the determination of amino acids. Under room temperature, pH6.3 HAc NaAc buffers, acetonitrile water solutions as the mobile phase and the use of the gradient elution mode, fine resolution of phenylthiocarbamyl derivatives of 18 kinds of common amino acids was achieved after about 30 minutes and the content of amino acids (except Trp) in the hydrolysate of protein of pearl was determined. The results showed that the proteins in pearls mainly consist of 10 kinds of amino acids such as Asp, Glu, Ser, Gly, Ala, Leu and so on which account for about 85 percent of total amount of protein.