Abstract: In this paper, a multilayer substrate integrated waveguide (SIW) four-way out-of-phase power divider is investigated. In a previous research (Eom , 2009), the four-way power division was studied by a 3-D mode coupling method, which was achieved by a vertical Y-junction as well as a lateral Y-junction of half mode substrate integrated waveguides (HMSIW) using a multilayer substrate. In this research, resistive coupling slots, for obtaining good isolation between four output ports and impedance matching at all the ports, are realized on the lateral HMSIW Y-junctions and the vertical HMSIW Y-junctions using isolation resistors. From the measurement results, excellent performances of insertion loss, isolation, impedance matching, and amplitude balancing were simultaneously achieved for the X-band range. It is expected that the proposed design of a multilayer substrate integrated waveguide (ML-SIW) power divider will play an important role in the future integration of compact multiway SIW circuits and systems.