Objective To observe the thoracic anatomic structure of rat for the experimental study of pectus excavatum. Methods Four younger and four adult Sprague Dawley(SD)rats were selected . The breath style, posterior-anterior and transverse diameter were recorded after general anesthesia. Gross and fault anatomic structure of chest was observed. Results (1) Diaphragmatic breathing was the main breath style and the anteroposterior diameter was larger than that of transverse. (2) The pleura and perichondrium were very thin; the sternum was divided into 4-6 segments connected with cartilage; the position of costochondral junction was at the posterior lateral side of rib anterior arch; there was only one lobe in left lung and four lobes in right. (3) A full and symmetric anterior chest wall was obtained and its heart in left posterior of sternum was not compressed in chest transverse section; the main structure between sternum and spine was heart, the anterior chest wall and sternum are no curve and depression in chest sagittal section. Conclusions There are remarkable difference of thoracic contour and the rib ring shape between SD rat and human being. The diaphragmatic muscle is more developed than that of chest wall in younger rat and the heart is in contact with anterior chest wall in a large area.