RFIDs in the UHF band are getting popular gradually in a lot of situations. Many kinds of small antennas have been contrived for UHF RFIDs. However, the antenna characteristics deteriorates in the case of using the antenna around water. In this report, a small cylindrical antenna was designed, which has little effect of water. The antenna is fed from an excitation loop outside of the radiation loop and the input impedance of the antenna is matched with complex the impedance of a RFID chip. The characteristics of the antenna are simulated and compared with those of a dipole antenna in order to evaluate the effect of water.