New designs of obtaining a dual frequency bands antenna operate on the dual frequency bands of Global Positioning System (GPS) and Global System for Mobile Communications (GSM) with a single-feed square micro-strip antenna are proposed and experimentally studied. The proposed designs are based on the different patch dimensions loaded with four rectangular slots in the form of cut from the sides of the square patch. The result of this work shows that the slots loaded into the square patch antennas offers further size reduction with multiband properties that can be used in GPS and GSM applications. Details of the design considerations of the proposed antennas are described, and experimental results of the obtained dual-band performances are presented and discussed.