Objective To establish a neonatal rat model of thoracic aortic dissection by treating pregnant rats with semicarbazide. Methods Implantable capsule osmotic pump with different concentrations of semicarbazide (5, 10, 15, 20, 25, 30, 35, 40 mg/\[kg·d\])or normal saline were implanted into the abdomen of rats on day 14 of pregnancy. The thoracic aortas of 21 day fetus and neonatal rats were collected. H-E staining was applied to examine the pathological changes under microscope, and the formation of thoracic aortic dissection was analyzed. Results Various degrees of thoracic aortic dissections were observed in neonatal rats after the mother rats were given different concentrations of semicarbazide. At a lowest semicarbazide release rate of 25 mg/kg per day, all the neonatal rats survived and had a high incidence of thoracic aortic dissection. Conclusion A neonatal rat model of thoracic aortic dissection has been successfully established, paving a way for further researches.