Wireless sensor networks (WSNs) are used in a variety of applications to sense and transfer information to the centralized node with energy efficiency increasing the network’s lifespan. Other factors, such as quality of service (QoS) is also important to improve the performance of the WSNs, by increasing throughput and reducing end-to-end delay. In this paper, we evaluate the importance of QoS in the Medium Access Control (MAC) protocol for WSNs using different metrics and parameters such as energy efficiency, throughput, delay, and the network lifespan. We propose a new QoS MAC protocol, “PRIority in Node” (PRIN), using static priority in the source and the intermediate node and priority among the node which is one hop from the sink node to achieve QoS in WSNs. Simulation results are compared with those of the synchronous MAC protocol in terms of QoS parameters to show the improved performance of the proposed MAC protocol.