This paper presents an active guarding circuit employing noise decoupling and inversion feedback for substrate noise suppression in high frequency up to GHz. Proposed inversion feedback circuit can efficiently suppress substrate noise up to GHz range by introducing a zero within an amplitude controller. The noise decoupling circuit not only provides a decoupling path, but also senses the noise level for the amplitude controller to perform noise cancellation. By applying the proposed active guarding circuit, the noise suppression of passive guard ring can be improved more than 14dB in the frequency range from DC to lGHz and 7.2dB up to 5GHz. For ldB degradation of noise suppression performance, the input noise level can be up to 90mV at 1MHz and 86mV at lGHz, respectively.