A new scheme to estimate the moment of inertia in the motor drive system in very low speed is proposed in this paper. The simple speed estimation scheme, which is usually used in most servo system for low speed operation, is sensitive to the variation of the machine parameter, especially the moment of inertia. To estimate the motor inertia value, Reduced-Order Extended Luenberger Observer (ROELO) is applied. The effectiveness of the proposed ROELO is applied by experiments.