A miniaturized partially-folded planar inverted F-antenna (PF-PIFA) is proposed for a wireless physiological data acquisition system, being developed for small rodents including rats. The system operates in the Australian 900MHz ISM band (915–928 MHz). The overall size of the antenna is 26×19×4.4mm³ and it has been designed to be implanted just under the skin of a rat. The 10dB return-loss bandwidth of the antenna is 2.8%, which is sufficient for this telemetry system. The RF link distance between the implanted and external antennas is assumed to be less than 2m.