A 13.56MHz high efficiency CMOS 1X/3X active rectifier with a novel active triple-voltage(3X) rectifier is proposed and verified. The proposed rectifier is specially designed for medical implant systems. It provides 1X/3X dual output voltage (1.99V and 6.29V) allowing the implantable neuromodulation system to operate with high power conversion efficiency (PCE) while stimulating simultaneously. A start-up control circuit is also added to achieve robust start-up mechanism. On-chip delay compensation control is implemented to increase the conduction time, avoid reverse current, and enhance the efficiency. In addition, the rectifier can sustain a higher input inductive voltage without the overstress problem by adding cascode power transistors. The measured dual output voltages of the 1X/3X rectifier are 1.99V and 6.29V while the input inductive voltage is 2.75V. The proposed rectifier achieves 84.2% in PCE with total 57mW output power under 13.56 MHz operation frequency. Based on its capability to provide large output voltage for stimulation with high PCE, the proposed 1X/3X active rectifier is suitable for implantable neuro-modulation systems.