This study concerns with the reasons of the revision of the classification scheme and the kinds and methods of the reclassification. The reclassification IS to be implemented in case that classification numbers are wrongly given, or the scheme is revised, or it is wanted that presently using scheme should be changed to a different one. In the case of a revised edition, it is desired that reclassification is made based on the new edition because of the modernization of a data organization. However, in case of that it is not possible for the situations in the library such as the number of collections, staffs, facilities, budget, etc., the old edition can be based and the new one can be referred to. In this case, however, classification numbers may be dualized on one subject, and therefore, library must prepare the reference cards and the marks of the shelves for the different class numbers. Also, because much budget is required when the scheme is changed to another one due to its unsatisfactory usage, it should be carefully considered whether to change or not. The required time in reclassification for the relocated classification number of the revised edition is 18 minutes 54 seconds per volume, and its cost requires W 1,224.