Dielectric ceramics have been greatly intended owing to their composition diversity and meeting the requirements of electronic industry and wireless communication. Among these ceramics, ceramic composites composed of a dielectric ceramic phase and a sintering aid glassy phase which offer dielectric features in the microwave frequency, have been utilized for application in the LTCC (low temperature co-fired ceramics) modules. The present work has been aimed to fabricate dielectric composites of mullite microparticles- ZBS (ZnO-B2O3-SiO2) glass for use as dielectric substrates in the LTCC technology. In this regard, composites with various volume ratios of mullite and ZBS glass were fabricated. Considering the sinterability evaluation at 950°C, composite of 50 mullite-50 glass (Vol. %) was chosen as the optimized sintered composite and focused for further examinations. Monitoring thermal behavior of the optimized composite during sintering by means of X-ray diffratometry and differential thermal analysis revealed that mullite reacts with glassy phase at about 880 ºC; results in the formation of gahnite (ZnO.Al2O3) phase. Microstructural observation confirmed prismatic morphology of the gahnite crystals dispersed homogeneously in the glass matrix. Dielectric characterization utilizing network analyzer showed the resonance of the optimized composite in the microwave frequency range. Dielectric permittivity (4.5) and quality factor (4704GHz) of the optimized composite is in accordance with the requirements of the targeted technology