Abstract: In two-tiered sensor networks, a storage node not only collects data items from sensors, but also deals with the queries from the sink. In a hostile environment, storage nodes may be compromised by attackers and then instructed to reveal sensitive data collected by sensors and reply incomplete or forged query results to the sink. A secure Top-k query protocol, named SecTQ, is proposed in this paper. SecTQ enables storage nodes to process queries correctly while preventing them from leaking the sensitive data collected by sensors. To preserve privacy, the direct comparison of data items collected by different sensors is transformed into the comparison of the collected data items and query-comparison value provided by the sink. Moreover a polynomial function-based preserving scheme is proposed to encode for both the data items collected by sensors and the query-comparison values of the sink, which allows the storage nodes to perform queries without knowing the actual values of both the collected data and query-comparison values. To preserve integrity, a linking watermark technology is proposed, so as to effectively verify the integrity of query results.