In this paper, a flexible dual-band open-loop antenna on inkjet-printed PET is proposed covering frequency spectrum of wireless local area network (WLAN). The dual-band property is fulfilled by an open-loop which served as two monopoles. And the PET inkjet-printed technology is used to reduce the fabrication run and achieves a mass production as flexible devices. The simulated bandwidths (return loss > 10 dB) achieved for the dual-band antenna are 2.29–2.50 GHz (∼8.75%) for the lower band and 5.55–6.05 GHz (∼8.62%) for the upper band. The center frequency of the two operation frequency are located at 2.4 GHz and 5.8 GHz with a minimum return loss of 17.5 dB and 29.2 dB, respectively. The simulated dual-band PET inkjet-printed open-loop antenna has a compact size volume of 28 × 37.5 × 0.1 mm3 (with feedline and backside ground), which can be easily integrated with other components.