A series of novel AB(3)-type monomers were prepared from nontoxic natural gallic acid and amino acids. These monomers were then melt-polycondensed in the presence of MgO as a catalyst via a transesterification process at 170-190 degrees C to yield the hyperbranched poly(ester-amide)s bearing terminal acetyl groups. FTIR and NMR spectra confirmed the structures of all the monomers and polymers. The degrees of branching, estimated from H-l NMR and quantitative 13 C NMR spectra, were 0.50-0.68. These hyperbranched polymers displayed moderately high molecular weights. Hydrolytic and enzymatic degradation studies were carried out in vitro at 37.5 degrees C in NaOH hydrotropic solution and in Tris-HCl buffer (pH = 8.6) containing proteinase K, respectively. The results indicate that the hyperbranched poly (ester-amide) s are degradable hydrolytically as well as enzymatically, and the rate of hydrolytic degradation increases with the pH value of the solution.