The BaZrO3 microwave dielectric ceramics with addition of x%B2O3 (x=0.5~5.0) were prepared using analytically pure BaCO3, ZrO2 and B2O3 as raw materials by traditional solid phase method. The effects of different B2O3 additions on microstructure, phase composition and microwave dielectric properties of BaZrO3 ceramics were studied by means of scanning electron microscope, vector network analyzer and X-ray diffractometer. The results show that the density sintering temperature, dielectric constant and dielectric loss decrease with the increase of B2O3 addition. The BaZr(BO3)2 phase precipitates when the added amount of B2O3 exceeds 1wt%. When the added amount of B2O3 is 3wt% and the sintering temperature is 1 300 ℃, BaZrO3 ceramics obtain excellent microwave dielectric properties, the dielectric constant εr=33.02, product of quality factor and frequency Q×f=32 761 GHz, temperature coefficient of resonant frequency τf=+152×10-6/℃.