In many Web search applications, similarities between objects of one type (say, queries) can be affected by the similarities between their interrelated objects of another type (say, Web pages), and vice versa. We propose a novel framework called similarity spreading to take account of the interrelationship and improve the similarity calculation. Experiment results show that the proposed framework can significantly improve the accuracy of the similarity measurement of the objects in a search engine. Categories & Subject Descriptors: H.3.3 [Information Storage and Retrieval]: Information Search and Retrieval - Search process, Clustering; H.2.8 [Database Management]: Database Applications - Data mining; I.5.3 [Pattern Recognition]: Clustering - Similarity measures General Terms: Algorithms, Experimentation.