Abstract A radio frequency identification (RFID) system was developed to monitor the movement of captive deer. Previous studies on the effect of repellent on deer behavior used video tape recording (VTR) to observe the movement of deer through a gate. A substantial amount of time was required to observe the VTR, and individual identification of the animals was impossible. Therefore, an automatic measuring system that enables identification of individual animals was required. The present experiment was performed using exhibition animals at a zoo. An injectable transponder was used to individually tag the animals because external tags, such as ear or collar tags, may have had a negative effect on the appearance of the animal. When a deer passed through the gates, the reader systems logged the transponder ID with a time stamp. A data processing program calculated the number of passages made by each deer from the ID data. The number of passages calculated by the RFID system was compared with that by VTR observation, and there were no significant differences. It is expected that this technology will have applications for behavioral monitoring of exhibition animals without disfiguring their appearance.