A particular UHF “miniaturized” antenna is presented in this paper. It is a kind of planar inverted F antenna (PIFA) which operates in a metal environment. The return loss of the antenna has been optimized over the ISM european frequency band (868 MHz). To reduce the size of the structure, the resonator has been folded under “itself” and a capacitive load is added in order to decrease the resonance frequency. The result is the achievement of an ISM - UHF Antenna matched at 868 MHz. The simulation results are obtained by the software design package CST Microwave Studio. The effects of various physical parameters are presented and discussed. The goal is to finally design an integrated device which will be able to communicate from a metal box.