Smart Grids are result of utilizing novel technologies such as energy storage systems, distributed generation, demand response resources, and communication technologies in power system to compensate some of its defects. Because of these technologies, various domains of power system will change. Power system operator will encounter various resources. Demand response resources which may be connected to distribution system or transmission system, distributed generation resources, energy storage systems, and renewable generations such as wind and PV farms are some of these resources. Power system operator should use a powerful methodology to manage these resources. Independent system operator should use a stochastic method to manage them. Stochastic unit commitment is presented in this paper to schedule various power resources such as distributed generation units, conventional thermal generation units, wind and PV farms, and demand response resources. Demand response resources which are connected to distribution network, Interruptible loads, distributed generation units, and conventional thermal generation units are used to provide required reserve for compensating stochastic nature of various resources and loads. In the presented model, resources connected to distribution network can participate in wholesale market through aggregators. Moreover, a three-program model which can be used by aggregators is presented in this article. Loads and distributed generation can contract with aggregators via these programs. A three-bus test system is used to illustrate usefulness of the presented model. The results show that ISO can manage the system effectively by using this model.