Effects of calcination temperature on microstructure and electric-magnetic properties of Mg-ferrite were investigated. As the calcination temperature increase, the green density and the sintered density increase due to the enhancement of densification of calcined powder. The grain size in the sintered ferrite increases with increasing the calcination temperatures from 800 to 100$0^{circ}C$, but decreases from 1000 to 120$0^{circ}C$. The resistivity decreases with increasing the calcination temperatures from 800 to 110$0^{circ}C$, but increases from 1100 to 120$0^{circ}C$ due to the microstructure which consists of small, uniform grian size and pores at grain boundaries. Magnetization increases slightly due to the increasement of the sintered density while Curie temperature is almost constant regardless of calcination temperatures.