In this paper, a circularly polarized (CP) microstrip antenna with vertical ground for RFID (Radio Frequency Identification) reader applications is presented. The proposed antenna is composed of a radiating patch on a substrate and a vertical ground surrounding four sides of the antenna. The vertical ground reduces the resonant frequency about 25 % comparing to that without vertical ground. Relatively good antenna gain of 5.6 dBi is obtained for such a small antenna. The results show that the proposed antenna has good impedance and radiation characteristics over the required bandwidth, 950-956 MHz (Japanese UHF RFID band). The dimension (100×100×13 mm3) of the antenna is suitable to use for a handheld PDA.