Implantable devices are getting great attention nowadays in order to improve patients ' nursing quality and to ensure their safety. Also, implantable antenna plays a vital part in transmitting data in medical devices. A compact PIFA antenna is proposed in this paper which is suitable for operation in 2.4 GHz ISM band (2.4-2.48) GHz. This antenna is designed using copper and Rogers RO3010 as patch and substrate, respectively. Overall dimension of the proposed antenna is only 9.48 mm ×7.8 mm × 0.25875 mm (19.1 mm3). Then it is encapsulated with Rogers RO3010 as superstrate to ensure safety. All the necessary simulations of the proposed PIFA antenna is done by using the CST Microwave Studio and optimized for better performance. The results are presented for both the rectangular and cylindrical phantom model to ensure suitability of the antenna for different types of implantable medical devices.