Bluetooth is a new developing wireless networking technology for short range applications. The basic unit in a Bluetooth network is piconet, which can contain up to 8 active nodes [1]. Two or more piconets may connect with each other to form the so-called scatternet. Scatternet is indispensable for the future of Bluetooth technology. One of the important issues for Bluetooth technology is security [8, 15]. Security protocols for Bluetooth piconets, such as key management and authentication have been defined by the Bluetooth Specification [1]. However, little work has been done on security of Bluetooth scatternets. In this paper, we propose a link key establishment protocol for Bluetooth scatternets by extending the piconet key agreement protocol to scatternets. The proposed protocol has the same security level as that of the piconet key establishment protocol and is compatible with the Bluetooth Specification.