Similarity search has been widely used in many applications such as information retrieval, image data analysis, and time-series matching. Specifically, a similarity query retrieves all data objects in a data set that are similar to a given query object. Previous work on similarity search usually consider the search problem in the full space. In this paper, however, we propose a novel problem, subspace similarity search, which finds all data objects that match with a query object in the subspace instead of the original full space. In particular, the query object can specify arbitrary subspace with arbitrary number of dimensions. Since traditional approaches for similarity search cannot be applied to solve the proposed problem, we introduce an efficient and effective pruning technique, which assigns scores to data objects with respect to pivots and prunes candidates via scores. We propose an effective multipivot-based method to pre-process data objects by selecting appropriate pivots, wh...