Abstract: In this paper, a high gain ultrathin UHF anti-metal tag antenna is proposed. The tag antenna is composed of upper metal patch with double T slots, dielectric substrate, and under metal patch. The plane size of antenna is 80 mm×40 mm and the thickness of it is just 0. 8 mm. The structure of proposed antenna is simple without short via, short patch and short pin. It is convenient to adjust the impedance of the antenna and realize low profile by modifying the dimensions of the T slots on the upper patch. The realized gain of proposed antenna is 3. 4 dBi without metal ground and 6. 9 dBi when it is attached to the metal ground. And there are no obvious changes in center frequency and impedance bandwidth of antenna. The measured results match well to simulated results. The measured identifying distance is 4. 5 m without metal ground and 6. 8 m when it is attached to the metal ground.