Significantly enhanced dielectric and loss characteristics have been observed in Ni0.4Zn0.6Fe2O4 ferrite with various Ba3Co2Fe24O41 (Co(2)Z) addition (x). Compared with pure NiZn and Co(2)Z ferrites, the composite ceramics obtain much refined grains and notable high-frequency characteristics. With the introduction of Co(2)Z into NiZn ferrite matrix, the resistivity is largely increased from the order of 10(6) Omega cm to the order of 10(8) Omega cm and the frequency stability of permittivity is dramatically enhanced. Co(2)Z addition obviously improves the magnetic quality factor Q and reduces the dielectric loss of the ceramics at high frequency. For the samples with x = 20-30 wt%, permittivity epsilon' is almost unchanged from 1 MHz to 1 GHz, Q is greater than 10 in a wide frequency range, and dielectric loss tan delta(epsilon) is observed to be of the order of 10(-3) at 100 MHz, which is lower by two orders of magnitude compared with pure NiZn and Co(2)Z ferrites. These characteristics are all desirable for magneto-dielectric ferrites in high-frequency applications.