Three-phase four-wire distribution systems are widely used in many countries. These power distribution systems are used for both three-phase three-wire loads and single-phase two-wire consumer appliances in South Korea, Myanmar and other countries. Unbalanced load conditions always occur in three-phase four-wire distribution systems. These unbalanced load conditions cause unbalanced voltages for three-phase and single-phase loads, and increase the loss in the distribution transformer. In this paper, we propose an active load balancer (ALB) based on constant DC capacitor voltage control for three-phase four-wire distribution systems. Constant DC capacitor voltage control is always used in active power line conditioners. The proposed control algorithm does not require any computation blocks to calculate the active and reactive currents on the distribution system. Balanced source currents with a unity power factor are obtained without any calculation blocks of the unbalanced active and reactive components on the load sides. The basic principle of the constant DC capacitor voltage control based strategy for the ALB is discussed in detail and then confirmed by digital computer simulation using PSIM software. A prototype experimental model is also constructed and tested to validate the feasibility of the proposed control algorithm. Simulation and experimental results demonstrate that the proposed ALB can balance the source currents with a unity power factor for a three-phase four-wire distribution system.