Economic feasibility of microturbine cogeneration systems in consideration of payback period as an evaluation criterion is investigated based on parametric analysis of the capital unit cost and power generating efficiency of microturbine cogeneration units. For this analysis, a method to clarify the relationships between the payback period and the aforementioned parameters by combining a nonlinear equation problem on the payback period with an optimal unit sizing problem to minimize the payback period. Based on this method, a map expressing the combination of the parameters for a target payback period is illustrated. Through numerical studies for a hotel, the economic feasibility of the microturbine cogeneration system is clarified and the annual primary energy consumption and CO_2 emission are evaluated.