Hemodynamic factors such as the wall shearstress play an important role in the pathogenesis and treatmentof cerebral aneurysms. In present study, we apply computationalfluid-structure interaction analyses on cerebralaneurysms with two different constitutive relations for aneur-ismalwall in order to investigate the effect of the aneur-ismal wall mechanical properties on the simulation results.We carry out these analyses by using two patient-specificmodels of cerebral aneurysms of different sizes located indifferent branches of the circle of Willis. The models areconstructed from 3D rotational angiography image data andblood flow dynamics is studied under physiologically representativewaveform of inflow. From the patient models analyzedin this investigation, we find that the deformations ofcerebral aneurysms are very small. But due to the nonlinearcharacter of the Navier-Stokes equations, these smalldeformations could have significant influences on the flowcharacteristics. In addition, we find that the aneurismal-wallmechanical properties have great effects on the deformationdistribution of the aneurysm, which also affects the wall shearstress distribution and flow patterns. Therefore, how to define a proper constitutive relation for aneurismal wall should beconsidered carefully in the hemodynamic simulation. In present study, we apply computationalfluid-structure interactions analyzes on cerebralaneurysms with two different constitutive relations for aneur-ismalwall in order to investigate the effect of the aneur -ismal wall mechanical properties on the simulation results. We carry out these analyses by using two patient-specific patterns of cerebral aneurysms of different sizes located indifferent branches of the circle of Willis. The models areconstructed from 3D rotational angiography image data and blood flow dynamics is studied From the patient models analyzed in this investigation, we find that the deformations of cerebral aneurysms are very small. But due to the nonlinear character of the Navier-Stokes equations, these smalldeformations could have significant influences on the flow characteristics. In addition, w e find that the aneurismal-wallmechanical properties have great effects on the deformationdistribution of the aneurysm, which also affects the wall shearstress distribution and flow patterns. Therefore, how to define a proper constitutive relation for aneurismal wall should beconsidered carefully in the hemodynamic simulation.