Wireless Sensor Network is application specific data centric networks, having application span ranging from house hold application to mission critical applications. Applications like fire detection require immediate attention from the base station. Further these networks are resource constrain networks which require efficient utilization of scare resources. IEEE 802.15.4 is one of the low power, low rate wireless personal area network standard which is specifically designed targeting resource constrain networks. IEEE 802.15.4 dose not support any prioritized scheme that creates hurdle when one uses it with mission critical applications. In our work we have extended IEEE 802.15.4 with explicit priority mechanism to adopt it for application specific prioritized packet delivery. Our simulation results of packet delivery, prioritized packet delivery and per bit energy consumption show that explicit prioritized mechanism out performs specified standard.