In this paper, effects of the parasite elements on an antenna impedance of a UHF RFID tag put on a high impedance surface (HIS) are experimentally studied in detail. It is shown that small parasite elements on a mushroom HIS structure can help to recover a mismatch of the impedance and this impedance recovery is brought by an in-phase frequency shift of the HIS due to a mutual coupling between the HIS and the parasite elements. The technique is applied to a commercial 953MHz band RFID tag inlet antenna on a 5×3-cell HIS with the total dimension of 125×75×1.5mm³ and it is demonstrated that the impedance mismatch is successfully recovered and the tag operates with a reading range of 3m even on a 200×300×2mm³ aluminum plate.