The present publication describes the development of an active UHF RFID localization system concerning small size RFID transponders with an integrated GPS module for fawn saving during pasture mowing. The localization of a conventional active UHF RFID transponder has obvious drawbacks in the needed hardware on the reader side. The transponder sends only its label and no additional position information is available at the reader. Therefore, a direction finding system and a received signal strength (rss) detector for distance estimation in addition to the reader itself is needed. The huge hardware effort required reader side can be prevented by developing a transponder with an integrated GPS Module for localization. Thus, the focus is on a small transponder design, which leads to a trade-off between the requirements of the desired performance and the realization of the localization system, consisting of an active GPS-UHF transponder and the corresponding reader unit. Especially the conditions for the communication between the transponder and the reader related to limited power supply has to be minded. Furthermore, the transponder realization is shown and the considerations were metrological demonstrated.