Wireless Sensor Network (WSN) consists of a large number of sensor nodes which are distributed over an area to perform local computations based on the information collected from the environment. In the network each node is equipped with a battery, which is almost very difficult to change or recharge. To save the energy and to increase the lifetime of battery powered sensor devices, this paper introduce a technique of adaptive sleep-wake up period. This sends sensor nodes to sleep mode when there is no data for transmission and makes the sensor nodes to wake-up before transmission takes place i.e. by dynamically changing the sleep-wake up period of each sensor nodes depending on the incoming traffic rate.