This study presents a bi-level framework to obtain optimal energy management of electrical energy storage (EES) units in power systems by minimizing the operation cost of the system to satisfy daily demand and by maximizing the benefit of storage units’ owner. Two agents are considered consisting of the power system operator and the owner of EES units. The former seeks to determine the minimum operation cost of the system in providing the system load, while the latter seeks to provide its maximum profit. The power system operator has the option to supply energy by the thermal generation plants or from the storage units. The proposed bi-level model provides optimal operation strategies for both the EES owner in the outer level and the power system operator in the inner one. In other words, the decision making of the power system operator is taken into account explicitly in optimal charge/discharge scheduling of EES owner in the introduced bi-level framework. The introduced bi-level approach is applied to the IEEE RTS 24-bus network in order to assess the performance of the model.