Due to low power density, it is difficult for a single-band rectenna to harvest enough power for IoT devices like wireless sensors. Thus to supply these consuming devices, harvesting RF energy from multiple frequencies is a solution to enhance the amount of harvested DC power. In this work, we introduce a triple-band rectenna, working at 900 MHz, 1.8 GHz and 2.1 GHz, three readily available bands in the ambience, for energy harvesting application. The proposed rectenna consists of three monoband rectifiers connected to a multi-band receiving antenna via a highly efficient triplexer. The antenna is made by superposing two concentric rings and manipulating their radii to achieve the desirable operating frequencies, with antenna gains of respectively 2.5 dBi, 4.5 dBi, and 4 dBi. The contiguous triplexer is made by connecting open stubs band-reject filters and optimizing their positions, resulting in the triplexing efficiency higher than 75%. The measured RF-DC efficiency under -10 dBm triple-tone input power is 40%.