A dual-band antenna adapted for an Ultra-mobile Personal Computer has a grounding element including a first grounding portion of elongated plate shape and a second grounding portion extending substantially perpendicular to the first grounding portion from a long edge of the first grounding portion. A connecting element is connected with the second grounding portion. An installing element is connected with the second grounding portion and spaced away from the connecting portion. A radiating element includes a low frequency resonator extending from the connecting element, a high frequency resonator extending opposite to the low frequency resonator and towards the installing element from the connecting element, and an enhancing frequency resonator extending from an edge of the installing element back to the high frequency resonator. The low, high and enhancing frequency resonators are substantially aligned with each other and parallel to the second grounding portion.