We measured the velocity profiles in an anatomically realistic model of a basilar tip aneurysm with small aspect ratio (depth / neck width) by LDV. We built an aneurysm model based on CT images. The maximum Reynolds number based on the diameter of basilar artery was 795 and the frequency parameter was 5.0. The inflow went into the aneurysm dome along the posterior wall. At the bleb, the flow separated from the wall and was decelerated. The outflow region was widely extended at the anterior side of the aneurysm with low velocity, because the dome shape developed asymmetrically to the anterior side. The shear stress at the bleb was intensified at the beginning of the deceleration phase, although the wall shear stress at intra-aneurysm points didn’t change drastically. We found out that aneurysms with small aspect ratio contains the peaked hemodynamic stress by using the realistic model. Therefore the diagnosis of aneurysm should be assessed by a realistic model.