Objective To investigate the activity changes of gelatinase in the formation of ascending aortic aneurysm. Methods Thirty five young Wistar rats were divided into two groups: the control group and the experiment group. The rat models induced by ascending aorta banding were made. The ascending aortas were taken after 3-5 months operation, changes of gelatinase activity was observed by gelatin zymography and film EM>in situ/EM> zymography. Results Gelatinase activity of ascending aortic aneurysm was significantly increased compared with that of normal ascending aortic aorta.Conclusion Elevation of gelatinase activity may play a significant role in the formation of ascending aortic aneurysm.