Key establishment is a fundamental service for secure communications between a central device and each biosensor implanted in the human body. It provides and manages the cryptographic keys to enable security services such as confidentiality, integrity and authentication. There exist several schemes to provide secure communications; however, some existing schemes employ unsuitable cryptography mechanisms or share a pre-deployed key in body sensor networks(BSNs). Due to stringent constraints of power, memory and computation capability, it is inadequate to apply asymmetric cryptography mechanisms to biosensors. Besides, it is also inappropriate to store the pre-deployed key in the implanted biosensor because, if the key is exposed, a person will have transplantation surgery for the secret to be redistributed. In this paper, we proposed the secure communication scheme only using symmetric cryptosystem without a pre-deployed key between a central device and each biosensor in BSNs.