Architectural heritages are exposed to natural and man-made disasters so that the need for research to prevent disasters has arisen. Cheomseongdae, known as the oldest astronomical observatory in East Asia, displays separation between the members and is tilted to the north-northeast. To diagnose the present conditions and to resolve problems, site investigations are performed. Boring is conducted in the surrounding ground of Cheomseongdae, and noninvasive investigations such as seismic tests and electrical resistivity surveys are conducted as well. The present study proposes a geotechnical engineering approach focused on noninvasive site surveys, and through this, relates current tilted condition of structure and provides information on the stability of Cheomseongdae. (C) 2011 Elsevier Masson SAS. All rights reserved.