Aneurysmal subarachnoid hemorrhage (aSAH) causes serious brain injury, and its mechanisms have not been completely unraveled so far. The causative factors for the brain injury initiated by an aneurysm rupture, which is referred to as the early brain injury (EBI), include elevated intracranial pressure, cerebral hypoperfusion, and blood contents that are directly exposed to the brain surface. At Day 4-14 post aSAH, delayed cerebral ischemia (DCI) often develops, which may worsen the neurological outcomes critically. DCI may be a consequence of EBI. Understanding the complex mechanisms underlying the post-aSAH brain injury (EBI and DCI) is, therefore, important in order to improve the neurological outcomes. In addition, several biomarkers possibly associated with EBI, DCI, and neurological outcome have been investigated, although none of these has been conclusive. A matricellular protein periostin has emerged as an important potential contributor to EBI and DCI, and may serve as the biomarker and a therapeutic molecular target for EBI and DCI. In the present report, the possible role of periostin in aSAH has been reviewed.