A new roller hearth kiln(RHK) has been developed, which satisfies not only the highest quality of Mn-Zn ferrites, but also large quantity of production. Using the RHK (the length is 50m), the total sintering time is reduced to less than 11 hours, that is shorter than the half of the case of pusher kiln. Then the productive capacity of the RHK achieved 100 ton per month. Moreover, the control of oxygen content during sintering and the subsequently cooling is performed precisely, so that two different types of Mn-Zn ferrite, i.e. high-permeability and low power loss materials, can be sintered simultaneously in the RHK. The electromagnetic properties of these materials reach to the highest level in mass production. This paper describes the basic structure and the characteristics of the new RHK, and shows the magnetic properties of Mn-Zn ferrites which are sintered by the RHK.