An Electrical Parking Brake (EPB) system is a device that operates to park the vehicle automatically with the push of a button insted of using conventional hand or foot levers which in some ways makes it the first by wire type of brake system. As such, it is being considered in some vehicle architectures as an automatic redundant backup for vacuum-less brake systems or autonomous cars. The EPB systems is generally divided into cable puller and motor on caliper (MOC) types. Recently , the MOC type EPB is being more widely applied in the global market due to product competitiveness and cost effectiveness. The MOC type EPB is composed of the caliper, torque member, pas assembly, nut assembly and acutator. Among them, the caliper has a structure which covers the nut assembly and is conneted to the actuator. When braking occurs, the reaction force caused by contact between the inner pad and disc compresses the outer pad to the disc inside the caliper. The torque member acts to support the vehicle's torque applied on the caliper and pad. As such, these two parts play a main role in the robustness of the EPB system and occupy more than 80% of the total weight. Therefore, optimal design of the caliper and torque member to maximize stiffness while minimizing weight is systematically important in the design of an EPB system. In this paper, stiffness and weight optimization was carried out for an EPB caliper and torque member starting out from basic shapes from production. The objective functions for the EPB caliper and torque member were designated as its weight and stiffness. Also EPB specific characteristics such as actuation force, actuator weight, and mounting requirements were considered. Main dimensions considered criitical from the previous design were taken as design variables. Design of experiments (DOE) procedure with tables of orthogonal arrays (OA) was used to set the levels of design variables and the effectiveness of each level was checked using CAE. Through discrete results, we were able to find continuous approximation models in a specified range. Based on the approximation regression model, design variables that could maximize stiffness under constant weight conditions were adopted. From this, it was possible to obtain an optimal design of an EPB caliper and torque member.