This study systematically analyzes the effect of various design parameters on the heat transfer and pressure drop characteristics of the heat exchanger with a slit fin. The Taguchi method, known to be a very reasonable tool in a parametric study, is employed in the present work. Only seven cases of experimental factors are considered because of the difficulty in producing samples and the manufacturing cost. Eighteen kinds of scaled-up models are made by compounding levels on each factor, and the heat transfer and flow characteristics of each model are analyzed. The results allow us to quantitatively estimate the various parameters affecting heat exchanger performance, and the main factors for optimum design of a heat exchanger are selected. The optimum design value of each parameter is presented and the reproducibility of the results is discussed.