In this article, the design of a resonator-based fat intra-body power transfer (Fat-IBPT) system has been presented for the application of implantable medical devices (IMDs). Herein, the low-loss properties of human fat tissue sandwiched between skin and muscle are considered to act as an effective waveguide for microwave power transmission. In the proposed implantable wireless power transfer (WPT) system, both the transmitting (Tx) and receiving (Rx) resonating elements have been placed in the fat layer of the human body model. The Fat-IBPT system is constructed to work in the industrial, scientific, and medical (ISM) frequency band of 2.40-2.48 GHz. The resonating structure is constructed by a planar circular spiral with a notch enclosed and excited by a loop antenna. During the numerical study, a three-layer human body tissue model (skin, fat, and muscle) is considered to optimize the resonator configuration by inserting in the fat layer. Also, to eliminate direct contact with the human fat tissue, a bio-compatible polydimethylsiloxane (PDMS) coating layer is considered all around the resonating structure. The wireless Fat-IBPT system is constructed by using two identical resonators, which act as Tx and Rx elements that have been placed in the fat tissue layer at different distances to show the power transmission. The concept of the proposed resonator-based Fat-IBPT system has been established by numerical studies. From the proposed Fat-IBPT system, maximum power transfer efficiency (PTE) of about 8.47 % has been achieved.