Recently the interest in miniaturization of mechanical devices has increased and magneto-rheological (MR) fluid brakes have been designed, fabricated and tested to be applied as a control element of various devices for assisting the elderly people. A multi-disk modular type of design is proposed to make an MR fluid brake that can generate high torque at the minimum size. The design parameters of the MR fluid brake were determined by mathematical modeling and the performance was predicted with magnetic analysis to maximize the design torque. A testbed was constructed and torque responses were measured and analyzed according to the input current for various rotational speeds to confirm the performance of the MR fluid brake. The experimental results showed that the MR fluid brake was applicable to actuating devices for assisting elderly people.