A dual band flexible antenna for applications at 900 and 2450 MHz is proposed in this paper. The antenna offers a compact size of 0.23λ o × 0.120λ o × 0.0007λ o , where λ o is the wavelength at the lower resonance. The antenna comprises a simple geometrical structure consisting of a W-shaped serpentine structure fed by a microstrip line, while a Defected Ground Structure (DGS) technique was utilized with a partial ground plane to achieve wide operational bandwidth. An additional capacitor was loaded in between the slots to achieve a higher resonance, thus resulting in a compact dual-band antenna. Various performance parameters were analyzed, and results were compared with the measured ones. The antenna offers good performance in terms of size, bandwidth, gain, and radiation pattern and thus increases the potential of the proposed antenna for both rigid and flexible devices.