This Paper represents the designing of the Tri- Band Rectangular Printed micro strip Antenna. One amongst the simplest feeding technique is employed i.e. coaxial feeding technique for feeding the antenna Tri band antenna is obtained by etching two quarter wavelength rectangular shaped slots inside the patch at the proper position to resonate over GSM, Bluetooth and Wi- MAX. The proposed antenna is realized on FR-4 dielectric substrate having a dielectric constant of 4.4 and loss tangent of 0.02, with dimensions of 46x38x1.6mm3. The design calculations are done for the frequency of 2.4 GHz. The designed antenna is simulated using EM simulation software CAD FEKO suite (7.0). The antenna covers the three bands of operation i.e. GSM (1.834-1.858GHz), Bluetooth (2.422- 2.487GHz), Wi-Max (3.519-3.583GHz) with reflection coefficient ≤-10dB. The overall simulation results shows that the antenna gives good impedance matching at desired frequencies with VSWR≤2.Also the radiation pattern, efficiency,gain and impedance for all four frequencies are investigated using simulation results.