This paper is about Comparative Analysis of Rectangular and Circular Microstrip Patch Antenna with slot using modified ground plane technique for UWB applications. Rectangular Microstrip patch antenna with rectangular slot and Circular Microstrip Patch Antenna with circular slot is designed for Ultra Wide Band Application. Then comparative analysis of both antenna is done in terms of Return Loss, VSWR, Gain, Directivity and Bandwidth of antenna. Microstrip feedline of 50Ω characteristic impedance is used to feed the patch. Modified ground plane technique is used to convert narrow band characteristics of Microstrip Patch antenna into wide band characteristics. FR-4 Epoxy Dielectric Substrate is used for design having e_r = 4.4 and having standard thickness of 1.58mm. The design was optimized by using CST Microwave Studio TM 2011 software to obtain most suitable configuration in terms of desired value of Return Loss, VSWR, Gain, Directivity and Bandwidth of antenna.