The advance of wireless technology has promoted the emergence of IoT. Specifically, RF energy harvesting can accelerate the development of IoT technology by enabling the miniaturized battery-less sensor nodes. For efficient energy harvesting, the impedance of the antenna and the rectifier should be matched. We present RectBoost, a dynamically adaptive matching network, for the optimum harvesting performance of rectenna. RectBoost monitors the output voltage of the rectifier and accordingly tunes the matching mode. By dynamically tuning matching networks, RectBoost helps the rectenna overcome early state impedance mismatch. RectBoost provides two advantages against prior works: output voltage and charging speed boost.