A sensor node hold small amount of resources in terms of processor, battery power, memory and communication range, but when a huge number of sensor nodes work together they are able to complete a good volume of task. It is just because of Wireless Sensor Network we are able to cooperate with physical world directly. In this context, hierarchical routing protocols offer energy-efficiency, scalability and reliability for WSN applications. With this goal in mind, this paper proposes to approve a Cluster-based approach for Energy-efficiency in the WSN (REER)protocol. The main purpose of REER is to provide energy-efficiency by using for cluster formation and a probability function for Cluster Head election. Simulations were conducted to show the benefits of REER compared with LEACH