This paper presents the integrated circuit design for a wireless bi-directional transmission micro-stimulator. This implantable device includes an internal RF front-end circuit, a control circuit, a stimulator, and an on-chip transmitter. The operation of this system is to receive a 2 MHz amplitude modulated signal generated by external circuits. This signal includes the power and data necessary for the whole internal circuit. Through the internal circuit, a stable DC voltage and digital data can be extracted to stimulate neuromuscular stimulation. Besides, the system can acquire biological sensing signals by means of an onchip transmitter. In this study, most of the integrated circuits for the implantable device have been verified by using Hspice simulations of a TSMC 0.25 /spl mu/m CMOS process technology implementation.