Densification, microstructures and dielectric properties of CaO-MgO-SiO2 glass-ceramics were investigated with ZrO2 nucleating agent using two-stage heat treatment in the low temperature co-fired ceramic (LTCC) method. The amorphous cullet (abbreviated as CMSZ glass) was synthesized by mixing CaO, MgO, and SiO2 powders with ZrO2 nucleating agent, which were melted at 1500 degrees C before the quenching process. The results show that CMSZ glasses annealed below the critical nucleation temperature (T-cn) and sintered at 950 degrees C exhibit obvious bloating phenomena. On the other hand, CMSZ glasses annealed above Tcn demonstrate that zirconia nucleation occurs at the first-stage heat treatment (annealing). The second-stage heat treatment (sintering) is characterized by the rapid crystal growth of CaMgSi2O6 phase around the ZrO2 crystallites, indicating growth of nuclei over the critical size above T-cn. Moreover, specimens fabricated using two-stage heat treatment and annealed above T-cn, exhibit appropriate microwave dielectric properties and high mechanical strength. (C) 2017 Elsevier Ltd. All rights reserved.