Glass-ionomer cements (GICs) are used in various applications in clinical restorative dentistry. In this study the effect of CaF2 content of the glasses on microstructure, thermal and mechanical behaviors of the synthesized glass ionomer cements was investigated. The results showed that by adding CaF2 at expense of SrF2 the first exothermic temperature (TE) of the glass was reduced from 735 to 704 °C and the compressive strength was increased from 42.0 ± 1.29 MPa to 60.3 ± 1.5 MPa as well. These substitutions led to extending of liquid-liquid phase separation in the glass. The enhancement of mechanical properties demonstrated through the process of annealing glass powder at temperatures below half of the glass transition temperature. This technique contributes to the improvement of mechanical properties by decreasing the residual stress and fostering the separation of amorphous phases. The formation of phase separation appears to be a significant factor in improving the mechanical properties of the oxyfluoride cements.