The purpose of this study was to compare effects of demineralization of citric acid and tetracycline HCI on periodontally involved root surface. Twelve periodontally involved single rooted teeth were used. After scaling and root planing, root conditioning with citric acid and tetracycline HCI were carried and the teeth were processed scanning electron microscopic observation.The results were as follows: The scaled root surface was covered by much debris and calculus. The effect of demineralization of citric acid and tetracycline HCI was more reduced on scaling group than root planing group, because of hypermineralization of cementum surface and demineralization effect on root surface of tetracycline HCI showed tendency to reduction. The root planed group displayed more smooth root surface than scaling group, the surface was covered by smear layer, thus no exposure of dentinal tubule opening and collagen fiber, especially after root planing, citric acid and tetracycline HCl treated group showed exposure of dentinal tubule and collagen fiber, thus it was thought that new connective tissue attachment could be acquired.