Objective To investigate the accuracy of electrocardiogram(ECG)-gated CT angiography in the detection of bleb in unruptured aneurysm. Methods In 2004,15 unruptured aneurysm patients received ECGgated CT angiography examination. Results Ten of the patients had bleb and the bleb was detected as the pulsation site in ECG-gated CT angiogram.Surgically excised specimen were stained and histological investigation revealed that there were partial or complete absence of tunica media smooth muscle and the internal elastic lamina layer in the aneurysm wall in 15 cases.A sudden reduction of collagen layer was noted in 10 cases with bleb.(Conclusion)ECG-gated CT angiography can be used in the bleb detection of unruptured aneurysms,and its accuracy can be verified by histological examination.