Tannin from acorn was identified by TLC and gallic acid in the tannin was determined by HPLC. The tannin extracted with methanol-butanol was not dissolved in ethanol, methanol for HPLC and water, while the tannin extracted with acetone-ethylacetate was so pure that it could be used for HPLC-running. The gallic acid showed a Rf -value of 0.39, the digallic acid of 0.21, the trigallic acid of 0.09, and the gallotannin of 0.00 respectively. The content of gallic acid in the tannin from acorn powder was 3.04%, from acorn starch, 0.90%, and from acorn starch gels, 0.64-0.86% respectively. The effect of tannin contents on the viscosity of acorn atarch was also studied. The maximum and cooling viscosity of the starch were decreased as the contents of tannin increased.