Solid-state compatibilities in the rich tricalcium phosphate and rich zinc oxide regions of ZnO-CaO-P2O5 ternary system were established through experimental studies. These are of special interest: the tricalcium phosphate region, for further bioceramic applications, and the zinc oxide region for applications related to other fields. The objectives of this work were to establish the effect of zinc oxide on stability, phase transitions, and microstructure; therefore different compositions ranging from 0.96% to 84% mol of ZnO were thermal treated and quenched at 900 degrees C. The crystalline phases and the microstructures were analyzed using X-ray Diffraction (XRD) and Field-Emission Scanning Electron Microscopy with Energy-Dispersive Spectroscopy (FE-SEM EDS). Moreover, refinement technique of lattice parameters using the FullProf 2k program and its graphical interface WinPLOTR enabled to establish the solid solution range of Zn2+ in beta-Ca-3(PO4)(2) on line joining Ca-3(PO4)(2)-ZnO. The results allowed to determine four compatibility triangles: ZnO-Zn-3(PO4)(2)-Zn2Ca(PO4)(2), ZnO-Zn2Ca(PO4)(2)-Ca-3(PO4)(2), ZnO-Ca-3(PO4)(2)-HAp, ZnO-HAp-CaO, and the three phase fields Zn-3(PO4)(2)-ZnO, Ca-3(PO4)(2)-HAp, and Ca-3(PO4)(2)-ZnO in the system.