This paper presents the design of a small planar loop antenna for applications in mobile RFID readers within cell phones. Compactness of the loop antenna, crucial to size reduction in the antennas designed for mobile handsets, is realized by bending a folded-dipole in a rectangle shape. Two arms are inserted to the loop antenna to increase the electrical length of the structure. Furthermore, a small parasitic patch is created at the back of the antenna to adjust the antenna impedance and to increas the electrical length. It's shown by simulation and experiment results that the antenna is efficient to reduce antenna dimension for UHF RFID reader.