Microstructure and permeability as a function of sintering temperature and composition were studied on the Ni$delta$Cu0.4-$delta$Zn0.6Fe2O4 ($delta$=0, 0.1, 0.2, 0.3, 0.4) which was prepared by Cu2+ substitution for Ni2+ in Ni.0.4Zn0.6Fe2O4, then followed by 8 wt% CuO and 1wt% Bi2O3 as sintering aids. It was found that NiCuZn ferrite in which Cu2+ is substituted for Ni2+ is more effective in reduction of sintering temperature than Ni.0.4Zn0.6Fe2O4, containing CuO as a sintering aid. The specimen $delta$=0.2 sintered at 90$0^{circ}C$ for 2hr exhibited the highest initial permeability value ($mu$o=280 at 1Mhz), but the real permeability decreased at the frequency under 10 MHz. EPMA analysis showed that Ni$delta$Cu0.4-$delta$Zn0.6Fe2O4 ($delta$=0.4), sintered at 95$0^{circ}C$ for 2hrs consisted of three phase regions of Ni.0.3Cu0.1Zn0.6Fe2O4 region, Cu and Bi liquid existed at the 3-point boundary, although the stabilization energy of Ni2+ is higher than that of Cu2+ in B site.