Objective To compare imaging features and to evaluate clinical values of aortic dissection(AD) with MRI and spiral CT.Methods MRI and spiral CT findings of AD in 18 cases confirmed by clinical or surgical pathology were analysed retrospectively.Results The sensitivity and specificity of two advanced techniques in diagnosis of AD were high.MRI and CT showed the dimension,true or false lumen,intimal flap,intimal tear,thrombus and intramural hematoma of AD,aortic dilatation or stenosis and the major aortic branches.Conclusion The two techniques are important for the suspect AD,two techniques are similar to display the features of dimension,classification,true or false lumen and aortic dilatation or stenosis,MRI plays an important role in diagnosis of AD and is better than CT in demonstrating the intimal flap,intimal tear,thrombus,intramural hematoma and the involvement of the major aortic branches,there were limitation in demonstrating calcification of intimal flap or vascular wall and emergency patients.