Control of the composition after heat treatment is important stage of biomaterials production especially in case of their new versions creation, because many biocompatible synthetic substances are unstable at high temperatures. Interaction between components in multicomponent systems is possible with the formation of new undesirable products. In this work, the process of calcination of composite granules with a variable content of hydroxyapatite and wollastonite and binder polymer (gelatine) was studied. It was found that materials heat treatment leads to a change of their phase composition caused by the apatite decomposition, transition of β-CaSiO3 to α-form, and calcium silicophosphate formation (in samples where apatite is the main component). Calcined products composition depends on the apatite/wollastonite ratio in the materials.