The effect of cationic surfactant, dodecylammonium chloride (DDACl), on the hydrolysis of octacalcium phosphate (OCP) was studied. The presence of DDACl inhibited, but did not stop, the transformation from OCP into a more basic calcium phosphate. DDACl inhibitory effect may be ascribed to the electrostatic matching between positively charged surfactant head groups and phosphate groups that are part of the Ca-OPO-Ca-OPO chain motif exposed on the side faces of OCP crystals.