In the Internet of Things (IoT), billions of physical devices are connected and provide a near real-time state of the world. By adopting a service-oriented computing paradigm, the capabilities of these devices (whether mobile or static) can be abstracted as IoT services and delivered to users in a demand-driven way. Service providers can have a comprehensive competitive edge by tailoring their services to match users' requests through a negotiation process, with the particular service provisioning specified in a service level agreement (SLA), which can be further used to monitor and guarantee the quality of service (QoS). The challenges for SLA negotiation in the IoT include the scale and the dynamics of the environment. Existing SLA negotiation approaches are focused on cloud computing, which do not consider the domain-specific properties of IoT services. In this paper, we designed a context-based negotiation strategy to evaluate offers and generate counteroffers, and integrate it with the WS-Agreement Negotiation standard. The evaluation results demonstrate that our proposal can produce a higher utility and maintain a good success rate compared to other negotiation strategies.