Mesoporous hydroxyapatite (HAp) rhombs were successfully synthesized by transforming CaCO3 into HAp via an ion-exchange reaction without any surfactants. The obtained HAp rhombs with mesoporous architecture exhibited high drug-loading capability and superior sustained release properties, and the drug release rate increased apparently with the decrease of the pH value of the solution medium, which make it a promising carrier for pH-responsive drug-delivery system.