Octacalcium bis (hydrogenphosphate) tetrakis (orthophosphate) pentahydrate [Ca(8)(HPO(4))(2)(PO(4))(4)center dot 5H(2)O] (OCP) consists of so-called "apatite" layers and "hydrate" layers. We have researched on the synthesis of layered OCP including various kinds of carboxylate ions. Calcium hydrogen phosphate dihydrate [CaHPO(4)center dot 2H(2)O] (DCPD) and alpha-tricalcium bis (orthophosphate) [Ca(3)(PO(4))(2)] (alpha-TCP) were mixed with respective carboxylic acid such as succinic acid, glutamic acid, aspartic acid, and citric acid which are bioactive organic compounds. The mixture was hydrolyzed to OCP including carboxylate ions after reaction for 24 h at 40-60 degrees C. We found that the OCP including bioactive organic compound is easily formed under the presence of carboxylic acid without any control of pH. It was observed that the synthesized products consisted of small sized thin layers. Thermolysis of OCPs including carboxylate ions did not show significant change in the structure at lower temperature than 400 degrees C. At 600 degrees C, they decomposed into hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2)] (HAp) and beta-TCP together with a small amount of beta-dicalcium diphosphate [beta-Ca(2)P(2)O(7)]. The respective amount of their reformed products depended on the content and the species of carboxylate ions incorporated into OCP. (C) 2008 Elsevier B.V. All rights reserved.