RFID tag antenna which could be mountable on metallic plate is designed and measured for 900MHz band. The proposed antenna consists of ground plane, substrate (εr = 4.7), feed line with shorted circuit and radiating patch with L-shaped slit. The feed line with shorted circuit is designed for the direct impedance matching between the antenna and the RFID microchip. Especially, it is possible to obtain considerably the easy impedance match with the proposed design. Overall dimension of the proposed antenna is 90×54×5mm3. When the antenna is placed in free space and mounted on 125×150mm2, 250×300mm2 metallic plates, the maximum reading distance is 6m, 4.8m and 5.2m, respectively.