Constructions and Architecture fields were divided into Architecture engineering and Architecture in the 5th edition of Korean Decimal Classification (KDC), but those were combined in the 6th edition of KDC published in 2013. The purposes of this study are to find problems and to suggest modifications through comparing and analyzing the 5th and the 6th editions of KDC, Dewey Decimal Classification, Nippon Decimal Classification and Universal Decimal Classification. The necessity of reclassification, a long classification number for History of Architecture and addition of categories of traditional building and architectural engineering are required to improve the 6th edition of KDC and the improvements and modifications of those problems are suggested.