Introduction: Cerebral aneurysm is a cerebrovascular disease resulting to subarachnoid hemorrhage. The generation, development and finally rupture of cerebral aneurysm could be related to hemodynamic stimulate, especially wall shear stress (WSS). WSS have been considered to play a role on the expression of such enzymes as iNOS, MMP-2 and MMP-9 leading to weakening of the arterial wall. However, detailed WSS distribution contributing to the enzyme expression has not been clarified inside cerebral artery. The purpose of our study is to clarify the WSS distribution corresponding to the enzyme expressions. Materials and Methods: We tried to induce cerebral aneurysm on rabbits, and created the realistic silicone model of the induced aneurysm. The flow field and WSS were measured using PIV (particle image velocimetry) and LDV (laser Doppler velocimeter) inside the realistic model. Furthermore, histological structure and enzyme expression were evaluated on the image of elastica van Gieson stain and on the immunostaining images. Results: Induced cerebral aneurysms were found in posterior circulation; the arterial bifurcation at basilar artery or posterior communicating artery. The induced cerebral aneurysm had an arterial wall structure with thinned media and lacked IEL. The thinned media was observed at the bulge top area wth low WSS distribution. On the other hand, lacked IEL was observed near the aneurysm neck area. Although WSS was not so low at the area of lacked IEL, the WSS spatial gradient appeared with high value at this area. The lack of occurs before the thinning of media on the process of aneurysm formation. In addition, MMP-2 and MMP-9 showed similar trend as the WSS spatial gradient. From these findings, high WSS gradient seems to have an effect on the early stage of cerebral aneurysm generation, stimulating the enzymes expression which leads to the destruction of the IEL.