This paper presents an image retrieval method based on region shape similarity. In our approach, we first segment images into primitive regions and then combine some of the primitive regions to generate meaningful composite shapes, which are used as semantic units of the images during the similarity assessment process. We employ three global shape features and a set of normalized Fourier descriptors to characterize each meaningful shape. All these features are invariant under similar transformations. Finally, we measure the similarity between two images by finding the most similar pair of shapes in the two images. Our approach has demonstrated good performance in our retrieval experiments on clipart images.