This final thesis explains the concept of radio frequency identification in detail, with special attention being drawn to the reliability of the operation of passive UHF RFID radio tags in the presence of metal surfaces. The frequency range of the system's operation is set to UHF of 868 MHz, with the remaining two areas on the LF and HF scales. Furthermore, the architecture of the RFID system contains three basic components, in which we classify the reader, the antenna and the radio tag, where the tag is precisely the component of interest in the continuation of the work. Considering the large application, of RFID tags in almost every branch of industry today, great flexibility is required, which is made possible through tags of different designs, including smart stickers, contactless smart cards, pendants, keys and others. After the theoretical processing of the data, the practical part of the work follows as part of several different measurements with the aim of testing the reliability of the RFID tags. The analysis is performed by measuring with six different types of tags placed on styrofoam and on metal, and markers placed at different distances (1-2 cm and 15 cm). Comparatively obtained results with real data collected in the laboratory, imply that Tag 2 is the most suitable for use on metal surfaces due to its design and properties.