Three Zn(II) complexes with nicotinamide(na), nicotinemethylamide(nma), and nicotineethylaniide(nea) were found to have in vitro insulinomimetic activities. X-ray structure analysis of [Zn(nea)(2)(H2O)(2)(SO4)], showed that each nitrogen atom of two nea molecules locates trans, and the two water molecules and each oxygen atom of the two sulfates coordinate to a Zn(II) ion, forming an octahedral geometry of Zn(N2O4) unit in an inorganic polymer crystal. The Zn(II) complexes with na, nma, and nea exhibited higher insulinomimetic activities, respective IC50 values (50% inhibition concentration of the complex in the free fatty acids release from rat adipocytes) being 1.34, 1.12, and 0.96 mM, than that of ZnSO4 (IC50 = 1.52 mM).