In this article, a novel wideband balun filter on the coupled slotline-line resonator topology with intrinsic balanced performance in magnitude and phase performance is presented. The proposed wideband balun filter consists of four uniform half-wavelength slot-line resonators (SLRs) in middle, one single-ended unbalanced port, and one balanced port with two terminals. By utilizing the distinct field conversion from the slotline to the microstrip line feeding line, the proposed technique can realize good balanced performance inherently in magnitude and phase over a wideband frequency range. In order to demonstrate the proposed scheme and support the design conception, one circuit prototype is designed, fabricated, and tested. All of the measured results of the frequency response, magnitude, and phase imbalance performance agree well with the simulated one, and these results have effectively demonstrated its good filtering property, intrinsic balanced performance in magnitude and phase over a wide band frequency.