This paper presents a novel design for a simple rectangular ring with an open-ended monopole antenna that is well suited to DCS/PCS/UMTS/WLAN applications for dual-band operations. A microstrip-fed rectangular monopole antenna is first designed and then modified to introduce the rectangular ring with an open-ended antenna and a rectangular slit in the ground plane. Prototypes of the proposed antenna were fabricated and tested. The antenna, resonating at 1,405 MHz and 4,840 MHz, has a -10 dB impedance bandwidth of about 1,695 and 1,530 MHz (1,220~2,815 and 4,495~6,025 MHz), or about 79.06 % and 29.09 %. The observed 2D radiation patterns and 3D gain performance of the antenna in the operation bands are discussed.