Thermostatically controlled loads (TCLs) have great potentials to participate in the demand response programs due to their flexibility in storing thermal energy. The two-way communication infrastructure of smart grids provides opportunities for the smart buildings/houses equipped with TCLs to be aggregated in their participation in the electricity markets. This paper focuses on the realtime scheduling of TCL aggregators in the power market using the structure of the Nordic electricity markets a case study. An International Organization of Standardization (ISO) thermal comfort model is employed to well control the occupants’ thermal comfort, while a rolling horizon optimization (RHO) strategy is proposed for the TCL aggregator to maximize its profit in the regulation market and to mitigate the impacts of system uncertainties. The simulations are performed by means of a metaheuristic optimization algorithm, i.e., natural aggregation algorithm (NAA). A series of simulations are conducted to validate the effectiveness of proposed method.