In this paper, a novel dual-band RFID/WiFi antenna designed with a one-sided planar structure is presented. The proposed dual-band antenna is fabricated and experimentally measured. The measured results are in good agreement with simulated results. The corresponding two passbands are recorded at 933 MHz and 2.398 GHz, with impedance bandwidth of 12.0% and 4.67%, respectively. Compared with the conventional 920 MHz RFID antenna, a size reduction of about 50% is achieved. With proposed antenna, an audio RFID postal box is designed and it is expected to provide some self services for the tourists in Macao.