Abstract: 16% tannic acid was selected as precipitation agent for the polymer protein over 2000Da in Fermented fishmeal. The contents of proteins and free amino acids in the filtrate of fermented fishmeal were determined by the fully automatic azotometer and automatic amino acid analyzer, and then calculated the contents of oligopeptides. The results showed that the recovery rates of low molecular weight proteins of 1500Da were 90%~95% and the relative standard deviation was 1.6%.