This paper proposes the application of multi-objective optimization to tap changing transformers in a distribution system. Conventional electrical power systems do not consider reverse power flow, in which the power flows toward the power system in distribution systems. When large quantities of distributed generators (DGs) are introduced into a distribution system they can cause voltage deviations beyond the statutory range, and can reverse flow toward the substation transformer. Consequently, this cause faults in electricity devices and even lead to a massive blackout. This is an important issue within the distribution system. To resolve voltage deviation problems it is necessary to consider some trade-offs. However, there is not much research adapting multi-objective optimization for use in the distribution system. Therefore this paper provides a method of multi-objective optimization in order to minimize voltage deviation while simultaneously minimizing the number of introduced voltage control devices and finding an optimum placement of those voltage control devices. Moreover, an optimum scheduling of the distribution system is adopted.