An automatic gain control (AGC) circuit composed of a variable gain amplifier (VGA), a peak detector (PD), and a nonlinear controller (NC) for digital hearing aid is proposed. To achieve low power consumption under 0.6-V supply voltage with threshold voltage Vth of 0.5 V, the AGC has been operated in the sub-threshold region with body-driven input. Moreover, the gate-degeneration and bump-circuit techniques are adopted to improve the linearity. The chip has been fabricated in TSMC 0.18-μm standard CMOS process, 52 dB gain range can be achieved under the measured results. Besides, the power consumption of the whole circuit is lower than 1.8 μW under normal conditions and the peak signal to noise ratio (SNR) is 39 dB. The core area of the AGC is 0.933mm x 0.828mm.