Abstract: For most index structures for XML data proposed so far, update is a problem because XML element's coordinates are expressed by absolute values. Due to the structural relationship among elements in XML documents, we have to re-compute these absolute values if the content of source data is updated. The reconstruction requires update of large portion of index files, which causes a serious problem especially when XML data content is frequently updated. In this paper, we propose an indexing structure scheme based on the Relative Region Coordinate that can effectively deal with the update problem. The main idea is that we express the coordinate of an XML element based on the region of its parent element. We present an algorithm to construct a tree-structured index in which related coordinates are stored together. In consequence, our indexing scheme requires update of only a small portion of index file in case of updating.