The biocompatibility of hydroxyapatite is appropriate for bone substitution, but its mechanical properties have to be improved. In this work, a natural deproteinized hydroxyapatite was combined with an endodontic cement, which is used as binder, has a short setting time and suitable mechanical characteristics, and is biocompatible with live tissues. Resorption properties of both the materials are different, but combining them, it is possible to make a new biphasic composite biomaterial with good mechanical properties, a short setting time, and controllable biodegradation. The new biocomposite was implanted subcutaneously in laboratory rats for eight and fourteen weeks, and thereafter its morphological alterations and contact with the live tissue were evaluated. A histological analysis showed that the implant had not caused inflammation and had been accepted by the live tissue. Microscopic examinations during the experiment showed that each fraction of the composite was resorbed in different times, and, in such a way, a porous structure of the implanted material was formed, which is essential for interdigitation of the hard tissue into the implant. In order to determine the mechanical properties of the new composite, it was tested in compression at different loading rates.