An operational problem is discussed for a gas turbine cogeneration plant in combination with a heat pump/thermal storage system that utilizes time-of-use pricing of the electrical utility. An optimal planning method is presented by which the operational policy of constituent equipment is determined so as to minimize the daily operational cost. An algorithm is proposed to solve this optimization problem efficiently by combining the dynamic programming method with the mixed-integer programming one. A case study is carried out to investigate the effect of introducing a heat pump system into a cogeneration plant.