In this paper, we investigate a microstrip patch antenna on a dielectric substrate with CSRRs employed in the ground plane, and examine the resonant frequency, impedance bandwidth, and radiation characteristics. The comparison of the impedance bandwidth between the microstrip patch antenna on a conventional high permittivity substrate and with the CSRR substrate is presented. The experimental results demonstrated that significant size reduction is possible for a microstrip antenna without sacrificing the bandwidth by using the CSRR loaded ground plane. The fabricated antenna achieves a 69% reduction in the resonant frequency as well as 67% improvement in the bandwidth compared to the conventional antenna.