In this paper, a wearable three-antenna system aiming for cellular Internet of Things (IoT) applications is proposed. The presented antenna system consists of two cellular antennas (LTE low-and mid-band antennas) and one GPS antenna designed by using the Theory of Characteristic Mode (TCM). Both the simulated and measured results with good agreements are provided in this work. As a result of successful excitation of chassis modes, the proposed cellular antennas can cover the desired cellular bands between 699-862 MHz and 1710-2155 MHz with corresponding wideband matching circuits. Meanwhile, the proposed GPS antenna operates with a good right hand circular polarization (RHCP) performance (at least 5 dB higher gain than left hand circular polarization (LHCP)). Reasonable isolation performances among three antennas are also gained due to utilization of orthogonal modes. The results also show that with the proximity of human body (wrist phantom), over the wideband operation bands all antennas can achieve good efficiency. The averaged levels of-10 dB,-6 dB, and-4 dB, respectively for LTE low band, mid band and GPS band are achieved, indicating its potential in future wearable cellular IoT applications. Index Terms-wearable antenna, Theory of Characteristic Mode (TCM), small mobile terminal antenna, wristband antenna I.