The reaction between the phenylphosphonate anion (PP) and the layered basic copper(II) nitrate (BCN), Cu-2(OH)(3)NO3, has been studied with the variation of initial pH (pHi; 2, 6, 11.5) and PP:BCN molar ratio (PP:BCN; 1:1, 2:1, 3:1, 4:1). X-Ray powder diffraction studies showed that the products (pHi of 2 or 6, PP:BCN of 2:1 or higher) were monophasic copper(II) phenylphosphonate (CPP) Cu(O3PC6H5).H2O. However, those from pHi of 2 or 6, PP:BCN of lower than 2:1 were polyphasic materials of the CPP phase and the BCN phase. The products (pHi of 11.5) were polyphasic materials containing the CPP phase and copper(ll) oxide phase which dominated at higher PP:BCN molar ratios. Elemental analyses of the monophasic products confirmed that two moles of phenylphosphonate anions reacted with BCN. Infrared spectroscopy and thermal analyses of the monophasic products confirmed the loss of nitrate and the presence of water molecules. The reaction appears to proceed through a coordinative mechanism and there was no evidence for the free phenylphosphonate anion.