Recent advancement in microelectronics and sensor devices have led to the development of a new family of networks called Internet of things (IoT). One of the challenges of IoT is the integration of autonomous and smart devices with multiple constraints specific to the wireless sensor network (WSN) environment. Among these constraints, the most important constraint is the energy efficiency of medium access control (MAC) protocol. To solve this problem, we propose an improved protocol called clustering based load adaptive MAC (CLA-MAC) for WSNs in IoT scenario, which involves mainly traffic load balancing  within each cluster to provide a tuneable trade-off between energy consumption, delay, and throughput. The proposed solution makes the MAC protocol more energy efficient by reducing competition between sensor nodes with the adoption of clustering scheme and traffic distribution, which can significantly reduce the probability of collision and idle listening. Simulation results indicate that the proposed approach performs better compared with load adaptive MAC (LA-MAC) protocol in typical IoT scenario.