The effects of B 2 O 3 addition on the microwave dielectric properties and the microstructures of (1-x)LaAlO 3 -xSrTiO 3 ceramics prepared by conventional solid-state routes have been investigated. Doping with 0.25wt.% B 2 O 3 can effectively promote the densification and the microwave dielectric properties of (1-x)LaAlO 3 -xSrTiO 3 ceramics. It is found that LaAlO 3 -SrTiO 3 ceramics can be sintered at 1400 o C due to the liquid phase effect of a B 2 O 3 addition observed by scanning electronic microscopy (SEM). The dielectric constant as well as the Qxf value decreases with increasing B 2 O 3 content. At 1460 o C, 0.46LaAlO 3 -0.54SrTiO 3 ceramics with 0.25wt.% B 2 O 3 addition possesses a dielectric constant ( r ) of 35, a Qxf value of 38,000 (at 7GHz) and a temperature coefficients of resonant frequency (τ f ) of -1ppm/ o C.