BaTi O (BT4) microwave dielectric ceramics using a copper electrode and containing 10 wt% BaO-ZnO-B O -SiO (BZBS) glass frit were sintered under reducing atmosphere at 950 °C and were investigated on the phase evolutions, microstructures and dielectric properties of BT4 with various BaO/SiO and ZnO/SiO ratios of BZBS glasses. Experimental results show that the BaO/SiO ratio contributes to wettability of glass with BaTi O ceramics, and ZnO/SiO ratio determines the densification of BaTi O ceramics. The different Ba-Ti-O and Ba-Cu-O phases with various Ba/Ti and Ba/Cu ratios can be attributed to the contents of BaO in glass. Ba Ti O and Ba Cu O may form when BaO contents are too high, and inducing copper diffusion due to the reactions of BaO and Cu, accompanying with degrading of the dielectric characteristics. If the ZnO contents of BZBS glasses were raised, a little bit of ZnSiO and Ba Cu O phases appear without Cu diffusion due to non-reaction of ZnO and CuO. The high ZnO/SiO ratio of glass reveals the lower softening point, indicating that the high ZnO glass could enhance the density and therefore increase the dielectric constant and quality factor.