The classical plastic injection method is based on the principle of injecting a single color of a single polymeric material into the mold cavity under high pressure. In cases where the products are expected to have contrasted functional features and different colors, the classic injection process and the conventional injection molds are not sufficient. This paper proposes a new design approach for multi-component injection molds required by products containing different polymeric materials or different colors of the same polymeric material at the same time. It also presents a case study including the design of the hot runner, electromechanical rotary-cross, cooling, and ejection systems of a two-component, eight-cavity toothbrush mold. The polymeric materials are polypropylene for the first component, and styrene based thermoplastic elastomer for the second component, which exhibit good bonding properties with each other. In addition, an analysis study covering the filling parameters and production defect generations is also provided. The adopted design approach provides a production rate of 1600 parts per hour, corresponding to 18 s cycle time and 200 cycles per hour, and makes it sufficient to rotate only the 80 kg core plate instead of 1120 kg entire core side. Compared to existing methods, the results show that the proposed multi-component injection mold design method eliminates the need for particular injection machines and robotic systems, shortens the cycle time, and reduces energy consumption.