In this paper, a four-way dual-band Gysel power divider (GPD)/combiner based on a back-to-back microstrip structure method is proposed and investigated. A two-layer substrate is adopted to implement this PD. In order to divide the input signal into four equivalent signals, the input and four output ports of the proposed PD are placed on the top and the four external isolation resistors are placed on the bottom layer of the substrate. Furthermore, the dual-band response is achieved by adding a short-circuit stub and an open-circuit stub to the structure. Then, the theoretical closed-form design formulas are derived based on the considered conditions and circuit transmission line theory. Finally, for verification purpose, a prototype PD is designed, fabricated, and measured which works at dual frequencies of 1 and 2 GHz simultaneously. The good agreement between simulation and measurement results, which show good impedance matching, isolation, as well as power transmission, verifies the correctness of the design theory.