The wearable multi-band antenna with tuning function for on-body and off-body communications is studied in this paper. It is a planar inverted-F antenna and there are two branches on the radiator: the longer branch low frequency band (950-956 MHz), and the shorter branch with a varactor diode embedded for high frequency bands. By supplying different DC voltages, the capacitance of the varactor diode varies, so the resonant frequency can be tuned without changing the dimension of the antenna. While the bias is set at 6 V and 14 V, WiMAX and ISM bands can be covered, respectively. In addition, the radiation patterns of the proposed antenna in 950 MHz, WiMAX and ISM bands are relatively omni-directional and are of no deep nulls in the half-sphere above the arm phantom. Therefore, the proposed antenna can be expected to be applied in on-body and off-body communications. In the future, we will try to increase the tuning range of the antenna and use the chest phantom in our study.