Abstract: Privacy preservation in wireless sensor networks has attracted more and more attentions. Computing MAX/MIN query result in wireless sensor networks while preserving data privacy is a challenge. This paper proposes a Zero-One (Z-O) encoding based Privacy-Preserving MAX/MIN query protocol in two-tiered wireless sensor networks (ZOPPM). In ZOPPM, sensor nodes in the query range firstly convert their sensory data into encoded data, by using Z-O encoding and hashed message authentication code mechanism, and send the encoded data to the corresponding storage node, and encrypt sensory data and send the ciphertext to it in the demand. According to the numerical comparison theory of Z-O encoding method, every storage node generates a local MAX/MIN sensor node in its own query cell, without sensory data in plaintext. Then, the storage node constructs a local query result when receiving the encrypted data from a sensor node, and sends it to the sink node. Finally, the sink node calculates the MAX/MIN query result after receiving the local query result from all storage nodes. The theoretical analysis and experimental results show that the ZOPPM protocol can ensure the privacy of sensory data and the query result, and it costs less energy consumption than other similar method.