Abstract: A QoS-constrained Deviation-Avoidance Tree with anchor node (Q-DATa) approach is presented in this paper. The Q-DATa approach can support efficient update/query operations as well as meet QoS constraints for the operations. The proposed Q-DATa approach designates, according to the QoS constraints, some anchor nodes that can aggregate and store the sensory data, so that the query from sink and the updates from sensor nodes are sent to the anchor node to meet their QoS constraints. A simulation study was conducted to validate the approach. The results show that Q-DATa inherits the merits from the DAT approach and also guarantees the QoS in terms of delay and loss rate requirements. Furthermore, on the weighted delay value, the Q-DATa approach outperforms the DAT approach, under most of the conditions. Keywords: WSN, Data Aggregation, QoS, Object Tracking