Morphological changes of microvessels in the cerebral cortices of Alzheimer's disease and control brains were examined. From several parts of the brains, all of the vessels in blocks of tissues were isolated with ultrasound treatment and mesh filtration, and were observed by light microscopy. The results obtained were as follows: There was no difference between the relatively large arteries of the brains with Alzheimer's disease and the control brains. However, in the Alzheimer's brain irregular shapes of blood vessels and degenerated smooth muscle cells of a single layer were observed in the terminal arterioles. In the capillaries, focal constrictions and irregular shapes were observed. In addition to these changes, the nuclei of endothelial cells were irregular and unclear. These findings seem to indicate that the degeneration of microvessels in the brain of Alzheimer's disease might have occurred at the terminal arterioles and the capillaries.