An ultra low power Op-Amp design is presented in this paper. In the proposed design, a gm enhancement technique is used to obtain sufficient gain and bandwidth. In the Op-Amp design, all transistors have been operated in weak inversion region. The proposed Op-Amp has been designed using UMC90nm library and simulated in Cadence analog design environment. The proposed circuit generates a 31dB gain, 52KHz UGBW and 69 degrees phase margin upon simulation, while the resultant power consumption is just 6nW.