For the purpose of investigation the response of the periodintal tissue in relation to the experimental tooht movement, the rats were inhibited from collagen formation by adminstration of aminoacetonitrile. Findings were as follows : 1) In experimental group, the principal fibers of the periodontal ligament came to run paralleal along thr alveolar bone or root surface on the pressure side, ot run parallel along the alveolar bone or root surface on thr pressure side, while the decrease in density, irregular arrangement, and partial loss of principal fibers were observed on the tension side. 2) Sharpey´s fibers at the alveolar bone decreased in number, and as the aminoacetonitrile administration continued, the capability of matrix formation decreased on the tension side, the narrowing of the alveolar septum and poor-bony trabeculation appeared on the pressure side. 3) In cementum, Sharpey´s fibers were distributed irregularly. The formation of acellura cementum was decreased on the tension side, while the formative capability of cellular cementum ws increased. 4) The degree of staining by Herovici technique decreased in the periodontal membrane. By PAS and ninhydrine-Schiff reaction it was appeared weakly positive in the region where the Sharpey´s fibers exusted.