To improve the microwave dielectric properties, CuO was doped into composite ceramics BaTi4O9-BaZn2Ti4O11 by the solid-state reaction. CuO worked as flux former and caused the liquid-phase sintering mechanism, which effectively improved the densification process and lowered the sintering temperature by nearly 100 degrees C. Moreover, Cu2+ substituted for Zn2+ sites in BaZn2Ti4O11 phase, which led to the increase of BaZn2Ti4O11 phase and the reduction of lattice parameters of BaZn2Ti4O11 phase, and both these two results had the positive effect on the dielectric properties, especially the Q X f value. As increasing CuO content from 0.0 to 3.0 wt%, the dielectric constant (er) increased from 35.5 to 36.5, the Q x f value increased first from 49 100 GHz to the peak value 62 600 GHz (1.0 wt% CuO) and thereafter decreased to 31 900 GHz, and the temperature coefficient of resonant frequency (tf) kept in a low value as <2.0 wt% CuO was added. At last, 0.85BaTi(4)O(9)-0.15BaZn(2)Ti(4)O(11) ceramics with 1.0 wt% CuO sintered at 1150 degrees C for 3 h showed excellent microwave dielectric properties: the high epsilon(r) = 36.4, the high Q x f= 62 600 GHz and the near-zero tau(f) = +0.2 ppm/degrees C.