In this study, a method to select a suitable source for total volume minimization in hybrid power source system (HPSS), which outputs power by combining a power-type and a energy-type source output, is presented. Minimized total source volume of HPSS are calculated using Karush-Kuhn-Tucker condition. In the calculation, total source volume is an objective function, the total output power and energy of HPSS are constraints and volume of energy-type, power-type source and power limitation of energy-type source are variables on the condition that energy-type and power-type source properties are constants. The study is conducted under the assumption of WL TC as a sample driving pattern. The total source volume of HPSS is calculated with several power-type source properties combination with a specific energy-type source. The results indicate using power-type lithium-ion battery as a power-type source reduces the total HPSS source volume the most and in typical power-type lithium-ion battery selected case, the total HPSS source volume is reduced by 25.0% compared to the source volume consist of a sigale energy source.