A miniaturized implantable microstrip split‐ring antenna (IMSRA) is proposed for wireless biotelemetry. The IMSRA takes up a miniaturized volume of 153.35 mm3 (10.5 × 11.5 × 1.27) and provides a dual‐band operation in 360 to 620 MHz and 2.32 to 2.54 GHz that covers The Medical Device Radiocommunications Service (MedRadio) (401‐406 MHz) and Industrial, Scientific, and Medical (ISM) (433‐434 MHz and 2.4‐2.48 GHz) bands. The principal part of the radiator consists of three homocentric split‐ring elements. In addition, three conductor paths located between the split rings are used for precise adjustment of the frequency. In order to reduce the antenna size, a shorting pin is appropriately inserted between one of the metallic rings and the ground plane. The impedance matching of the antenna is improved by the use of a hook‐shaped slit placed on the ground plane. For verification of the in vivo operation, the proposed IMSRA was measured in two separate skin‐mimicking gels for MedRadio and ISM bands. A prototype was also tested in the skin tissue sample of a donor rat. The proposed antenna offers 53% (360 ~ 620 MHz) bandwidth at 490 MHz and 9% (2.32 ~ 2.54 GHz) bandwidth at 2.43 GHz. The IMSRA exhibits well‐behaved radiation patterns and SAR values at the respective bands.