In this letter, a low-profile 90° polarization rotator with a fourth-order bandpass filtering response is proposed by using aperture-coupled patch resonators elements. The presented polarization rotator is constituted on a five-layer structure consists of two orthogonal rectangular apertures etched on two different layers, and are sandwiched between two single-mode square patch resonators and a dual-mode corner-truncated square patch resonator. Moreover, the property of 90° polarization rotation is obtained by properly exciting two orthogonal modes within the corner-truncated square patch resonator and the polarization selective characteristic of two orthogonal rectangular apertures. The proposed polarization rotator is designed and analyzed with the direct coupling matrix method. To validate the design concept, a design example is fabricated and measured. Measured results well reveal that our proposed structure has its attractive advantages of ultrathin profile, high-order filtering response, high polarization purity, and stable performance under oblique incidence.