For the purpose of understanding the mechanism of the reaction between tannin and poly(N-hydroxymethylacrylamide) (pNMA) reported in the preceding paper, corresponding elemental reactions of catechin and tannin with N-(hydroxymethyl)acrylamide monomer (NMA) were studied. NMA reacted with both catechin and tannin under acidic conditions, and analyses of the isolated products by NMR and mass spectra revealed the chemical structures of the adducts, supporting the effective adhesion shown in the preceding work. The evidence indicating the decreased solubility of the adduct in water explains the enhanced water resistance of bonding by the tannin-pNMA adhesive.