Effect of ceramic processing was investigated on the microstructure and electronic properties of low loss Mn-Zn ferrite. Addition of CaO and SiO2 to calcined powder rather than to raw materials mixtured resulted in finer-grained microstructure. Higher oxygen pressure during sintering caused microstructural inhomogeneity and the increase in power loss and disaccommodation factor. Relatively low power loss was found for sintering up to 130$0^{circ}C$ from powders calcined at high temperature and milled shortly. It was caused by slow densification rate and normal grain growth up to 130$0^{circ}C$. Calcination at low temperature and prolonged milling enhanced den-sification, which gave a fine grained microstructure and low powder loss at sintering temperture below 120$0^{circ}C$. Sintering temperature above 125$0^{circ}C$, however, showed abnormal grain growth.