The ability to sinter a complex bioactive glass three-dimensional porous structures is of great interest in context of bone regeneration or templates in tissue engineering. Thermal treatment of bioactive glass ceramics dictates many important features such as microstructure, degree of crystallinity, mechanical properties, and biological response. In this context, herein, we investigated the effects of thermal treatments on crystallization of sol-gel derived 45S5 bioactive glass. Temperature and time of the thermal treatment strongly influence the formation of different crystalline phases. Combeite (Na2Ca2Si3O9) crystallizes as the primary crystalline phase along with a calcium silicate‐phosphate (Ca15(PO4)2(SiO4)6) phase, which decomposes into rhenanite after prolong thermal treatment. Our results provide a basic platform for tailoring the crystalline phases by controlling the nucleation and growth of crystalline phases via thermal treatments.