An improved guarding circuit is applied to a transconductance driven-right-leg circuit to decrease common-mode current at measurement electrodes due to power-line interference. After showing conventional guarding circuit is instable due to gain-peaking when used with a transconductance DRL circuit, the effect of the proposed guarding circuit modified to suppress the gain-peaking by inserting a series resistor between shields and a shield driver was analyzed. It is shown that, besides stability, the proposed guarding circuit provides two other advantages: 1) The gain of the shield driver can be set to be unit nominally. 2) The loop gain of the transconductance DRL loop can be increased due to pole-zero canceling. The proposed circuit was implemented and the advantages were confirmed.