Abstract: The major dimension parameters of the single band IFA are analyzed first, and the results of their impacts on both impedance and resonant frequency of the antenna are given as well. Based on the results, the prototype dual band IFA for 2.45GHz and 5.25GHz is designed, and the novel transformed dual band IFA structure is presented with the corresponding simulation and experimental results. The proposed antenna is simple and flexible to design, and can be printed on the FR 4 board directly for its compact profile, resulting in cost effective manufacture and convenience to feed. Further more it has high radiation efficiency, omni directional pattern and mixed polarization, which make it not only fit for the current but also the future generation WPAN/WLAN systems.