Wireless medical sensor networks is a key enabling technology in e-healthcare that allows the data of a patient’s vital body parameters to be collected  by a wearable or implantable biosensors. The major issue is the security and privacy protection of the collected data because of the resource constraints in the medical sensor network devices. There is a high demand for both security and privacy in practicality. Here we propose a lightweight and secure medical sensor networks. The technologies used in this system are hash-chain based key updating mechanism and proxy protected signature technique. The important feature of hash-chain based key updating mechanism is that for each transmission of data the key is updated.  These technologies are helpful to achieve efficient secure transmission and fine-grained data access control. This system also provides the backward secrecy and privacy. This system requires symmetric key encryption/decryption and hash operations .These techniques are suitable for low power sensor nodes. This is the best secure data transmission a access medical sensor networks.