Four regiospecifically methylated condensed tannin derivatives were synthesized by the condensation of regiospecifically methylated flavan-3, 4-diols protected by benzyl groups, and subsequent debenzylation. The monomeric flavan-3,4-diols were obtainedviafour reaction steps starting from phloroacetophenone derivatives and protocatechualdehyde derivatives. Protein—precipitating capacity of these synthetic condensed tannin derivatives was tested and a comparision of these capacity suggests the following results: 1) Phenolic hydroxyl groups in tannins are essential sites for protein precipitation. 2) Although the A-ring has been considered not to be important for tannin—protein interactions, it was proved that the A-ring also plays an important role together with the B-ring. 3) Both hydroxyl groups of A- and B-rings may synergistically interact with proteins.