To co-fire with commercial LTCC (Low Temperature Co-fired Ceramic) materials at 850oC ~ 880 oC, different contents of B2O3 were added to the Bi2O3-ZnO-Nb2O5 (BZN) ceramics. The dielectric properties of BZN ceramics sintered at low temperatures were studied. According to the test results, the cubic phase of BZN was transformed into orthorhombic in all the test materials. A BiNbO4 phase was formed in test materials with 2 ~ 5 wt% of B2O3 addition. The BiNbO4 phase was inhibited by extra ZnO addition. The phase transformation of cubic BZN was controlled during the synthesis process of cubic and orthorhombic ZnO-Nb2O5 phase with excess ZnO content. The Cubic and orthorhombic phases of BZN could coexist and be sintered densely at 850 oC/2hr.