This experiment was performed to study the effect of prostaglandin E<sub>²</sub> on tooth movement and root resorption in orthodontically treated cats. Twenty five cats were divided into five groups and closed coil springs delivered 80gm were stretched between upper canine and 3rd premolar. 10µg of PGE<sub>²</sub> was injected locally in the submucosal area of the upper right canine, while the left side served as a control and was injected saline 0.1ml. The distance between canine tip and central cusp tip of the 3rd premolar was measured. Scanning electron photomicrographs were made of the coronal half of the distal root surface of canines and cemental craterings were observed and quantified using point-counting volumetry. Data were analyzed by 2-way ANOVA and paired t-test. The results were as follows: 1. The rate of tooth movement of the PGE<sub>²</sub> side was increased, particularly at 1 day, compared with the control side. 2. The rate of tooth movement was minimum from 7 days to 10 days. 3. The resorption of root surface of the PGE<sub>²</sub> side was decreased from 4 days to 10 days, compared with the control side.