Wireless sensor networks are often deployed in hostileenvironments. Protecting the communication against node capture is oneof the most important design objectives. Focused on the revocations ofresource constrained nodes, an efficient leveled group key managementscheme is proposed. This scheme is based on a novel application of ana-ary logical key tree. Since sensor nodes may leaveor join the WSN frequently, a sublevel session key is introduced toprotect the sensitive information transmitted in the network. In aleave event, the remaining legal sensors in the key tree arepartitioned into disjointed subtrees. The group key can be updatedsecurely by encrypting the new group key with the common keys shared bythe sensors in the same subtree. When a sensor requests to join thecommunication group, it is assigned a sublevel session key which isused to communicate with GCKS and other legal sensors. The currentsession key is sent to the new sensor only after it gets the trust ofGCKS. This scheme is scalable, stateless and simple to employ.