In this article, a novel quad-band fractal PIFA antenna design for DCS, PCS, UMTS, and WiMAX wireless communications systems is presented. The proposed antenna is a PIFA antenna where a slot having a Hilbert fractal shape at the third iteration has been inserted at the center of the radiating patch. The fractal shape of the implanted slot on the PIFA antenna was used in order to make the antenna operational at four frequency bands, according the required applications. The proposed antenna with the fractal shape of the slot offers quad-band operation with a miniaturized size compared to the initial PIFA antenna, such that the dimensions of the radiating patch become equal to 28 mm × 28 mm. This structure is operational in the following frequency bands: (1.73–2.08) GHz, (2.46–2.59) GHz, (3.39–3.47) GHz, and the band (4.56–5.02) GHz covering DCS, PCS, UMTS, and WiMAX mobile communications systems, respectively, with a gain ranging from 2 dB to 6 dB at the desired frequency bands. The fractal PIFA antenna design was carried out under CST MWs software with validation of the results made using HFSS software. There is good agreement between the obtained results by the two simulation software.