A wideband vertical microstrip-To-microstrip transition has been proposed in this paper. Two dual-mode slotline resonators are placed on the common ground between the top-and bottom-layer to construct a novel wideband transition. The first two resonant modes in the slotline resonators are excited and utilized by coupling or feeding them at specific positions. After resonators themselves and their coupling scheme are decided by the split-mode graph, I/O coupling structures are implemented by using the microstrip-To-slotline cross-shaped transitions. Finally, the well-designed transition is fabricated and measured to support the validity of the structure. The measured transition has an operating bandwidth of 100.0% with in-band return loss higher than 10.8 dB.