An ultrahigh-frequency RF identification system, consisting of a fully integrated tag and a special reader, has been developed for short-range and harsh size requirement applications. The system is fabricated in the standard 0.18-μm CMOS process. The whole tag chip with an antenna, an analog front end, a baseband, and memory takes up an area of 0.36 mm2, which is smaller than other reported tags with an on-chip antenna (OCA) using the standard CMOS process. A self-defined protocol is proposed to reduce the power consumption and minimize the size of the tag. A specialized system-on-a-chip reader system, consisting of RF transceiver, digital baseband, MCU, and host interface, supports both the self-defined and International Standards Organization 18000-6 C protocols. Its power consumption is about 500 mW, which is much lower than other reported readers considering the transmission power. Measurement results show that the system’s reading range is 2 mm with a 20-dBm reader output power. In addition, it has been verified that the data stored in the OCA tag embedded in a pearl can be successfully read out. With an inductive antenna printed on a paper substrate around the OCA tag, the reading range can be extended from several centimeters to meters depending on the shape and size of the inductive antenna.