A mechanically flexible wireless power transmission module for implantable systems with enhanced transmission efficiency using a closed magnetic circuit (CMC) is presented. The CMC-based power transmission module consists of a primary inductor for power transmission and a secondary inductor for power reception. The CMC is fabricated by electroplating the Permalloy, composed of 81 nickel and 19 iron, on the inductors. For an open magnetic circuit (OMC), the measured power transmission efficiency was 13 when the distance between the two inductors was 5mm. However, the efficiency was enhanced to 27 and 34 for the proposed two types of CMCs.