Even if 960 o C is used as sintering temperature, the undoped BiNbO 4 ceramics are difficult to be densified. The addition of CuO will improve the densification process of BiNbO 4 ceramics. As the amount of CuO addition increases from 0.125 to 1.5 wt%, the dielectric constants ( r ) of densified BiNbO 4 ceramics decrease from 43.9 to 42.8 and the temperature coefficients (τ f ) change from -4.5 to -31.2 ppm/ o C. The quality values (Q) first increase, reach a maximum at 0.5wt% CuO, and then decrease with the increase of CuO amount. In CuO-doped BiNbO 4 system, BiNbO 4 ceramics with 0.5wt% CuO added and sintered at 920 o C have the optimum microwave dielectric properties: ( r =43.6, τ f =-20.8 ppm/ o C, and Q=1610 (Qxf=10070)