In this paper, we present a novel and implantable micro-stimulator design. Instead of generating the stimulating pulses by using the conventional computerized controller such as FPGA or MCU, the pulse width modulation (PWM) has been used to control the stimulation. The proposed system need not program the computerized controller, so it simplifies the circuit complexity and achieves the low-cost issue. The proposed micro-stimulator chip has a 5-bits programmable current selectivity and uses pulse width modulation skill to adjust the pulse width. Besides, the system has four different stimulation frequencies to be chosen and provides normal, random, and burst stimulation pulses for the practical situation.