We have investigated the effect of the Ca/P molar ratio in the starting composition on the synthesis of octacalcium phosphate intercalated with dicarboxylate ions (OCPC), starting from calcium carbonate and phosphoric acid in the presence of a dicarboxylic acid, such as succinic acid, adipic acid, or suberic acid. For a Ca/P molar ratio in the starting composition of 1.6, which is the stoichiometric value for OCPC, the highest yield of OCPC with a high degree of crystallinity was obtained for the OCPC samples synthesized with starting Ca/P molar ratios of 1.5, 1.6, and 1.7. The Ca/P molar ratio of the starting composition is an important factor in the synthesis of OCPC. This synthesis route provides for the effective production of OCPC samples.