This study is aimed to investigate the solid state reaction using monoclinic zirconia (m-ZrO2) and calcium aluminate cement (CA), as starting materials. Various compositions, containing different proportions of CA (5 - 15 mass % CA in ZrO2), were reaction sintered at 1300 - 1500°C. Crystalline phase formation and densification of CaO stabilized ZrO2 composites were investigated by X-ray diffraction (XRD) analysis, density and shrinkage measurements. Scanning electron microscopy (SEM) was used to examine the microstructure. Mechanical characterization was carried out by three-point flexural test measurements. As a result, sintering of mixtures of m-ZrO2 with CA as a source of CaO at 1300 - 1500°C was effective to produce Ca stabilized ZrO2 composites. XRD results indicated that during sintering, calcium coming from calcium aluminates decomposes and reacts with zirconia forming a tetragonal zirconia (t-ZrO2) structure.