An ultra-low voltage rail-to-rail operational trans conductance amplifier (OTA) based on a standard digital 0.18μm CMOS process is described in this paper. Techniques for designing a 0.6 volt fully differential OTA are discussed including bias and reference current generator circuit. To rail-to-rail operation complementary input differential pairs are used where Bulk driven technique is used to reduce the threshold limitation of the MOSFET transistors. The OTA gain is increased by using auxiliary gain boosting amplifier and a inverting amplifier. The designed circuit was simulated by HSPICE software and 0.18 micrometer technology. This circuit is supplied with 0.6 v with a consume power of 30 microwatt and open loop gain voltage of 63 dB.