Hypoxic condition in the brain result in microvascular dysfunction. Pericytes are one of the blood-brain barrier constituents with the endothelial cells and astrocytes. Pericytes of blood-brain barrier are the first cells to react to hypoxia of brain. We showed, at the ultrastructural level, microvascular pericyte responses to the brain hypoxia in early stage of hypoxia in cats. In first 2 h of hypoxia, pericytes start to migrate and one of every three pericytes migrates from original location. In the first stage of migration spikes occur at the abluminal surface of pericytes. At the same time basal lamina thickens and endothelial cells remain the same.