A dual-band implantable complementary split-ring (CSR) antenna is proposed for Medical Implant Communication Services (MICS) and Industrial Scientific and Medical (ISM) bands biotelemetry applications. The proposed antenna is printed on a grounded RO3010 substrate and the total size of the compact design is only 14 x 14 x 1.27 mm(3). The metallic top layer of the antenna is composed of three homocentric rectangular CSR elements and slots inserted between the rings. While the slots are used for fine frequency tuning, a shorting pin appropriately placed between the top copper radiator and the ground plane is utilized for miniaturization purpose. In order to improve impedance matching and enhance bandwidths of the antenna, we employ a hook-shaped slot in the ground plane. The proposed implantable CSR antenna (ICSRA) is fed by a coaxial probe. The proposed ICSRA was fabricated and measured in two different gels mimicking the real human skin tissue at the MICS and ISM bands. Also, a prototype of ICSRA was measured in a real skin sample obtained from a donor rat for in vivo verification. The ICSRA provides 23.5% bandwidth at 460 MHz and 12% bandwidth at 2.34 GHz and it exhibits acceptable radiation pattern characteristics at the respective bands. The specific absorption rate values of the antenna satisfy the limits set by standard safety guidelines.