A single feed compact rectangular microstrip antenna for tri-band application is presented in this paper. Two T-shaped slits are introduced at the edges of the patch to reduce the resonant frequency. For the proposed antenna three resonant frequencies are obtained at 3.35GHz, 5.29GHz and 7.65GHz respectively. The antenna size has been reduced by 66% with respect to the first resonant frequency in comparison to the conventional antenna. The design and simulation of the proposed antenna is carried out using MoM based electromagnetic solver IE3D.