<p>This article presents the design of a miniaturized bandpass filter featuring a square patch perturbed microstrip resonator configuration with the Swastik fractal slots for applications in the terahertz regime. In the proposed design, the dual-mode behaviour of the filter is demonstrated with two transmission zeros on the passband edges, leading to a substantial improvement in selectivity. Besides, the presented terahertz filter, using a full-wave electromagnetic simulator, exhibits appreciable size reduction through the integration of Swastik fractal slots into the resonator, realizing miniaturization without compromising the desirable filter characteristics. Through proper optimization of the filter dimensions such as the perturbation and gap size, significant enhancements are also achieved in its return loss, insertion loss, and selectivity. The bandpass filter, measuring 8 × 8 µm², demonstrates notable performance at 3.88 THz with a return loss exceeding 38.32 dB and a low insertion loss of 1.63 dB. Furthermore, the presence of transmission zeros at 2.86 and 5.14 THz, on the left and right sides of the passband, indicates better suppression of out-of-band frequencies. The minimal footprint and better performance of the filter make it an ideal candidate for integration into the terahertz system, thereby enhancing the capabilities of terahertz-based communication and imaging technologies.</p>