Abstract: For the data privacy in wireless body area network (WBAN), a secure privacy preserving k-nearest neighbor (kNN) query protocol for WBAN is proposed. This protocol can protect data privacy and access control by encrypting both data and queries with asymmetric scalar-product-preserving encryption (ASPE). To improving searching efficiency, we combine the technologies of R-tree and bucket partition and propose a data structure, named BRtree, for indexing data items. BRtree can significantly eliminate the unnecessary searching branches. In order to achieve access control, we separate an access key from the encryption key and introduce a trusted third authority to manage access rights and access rights transferring. The experimental results validate the efficiency of our scheme.