The relationship between the poststroke blood pressure (BP) and functional outcomes in patients with acute ischemic stroke is still controversial. The aim of the present study was to elucidate the impact of the poststroke BP on the clinical outcomes of acute ischemic stroke. Among the patients in the Fukuoka Stroke Registry, 1874 patients with first-ever acute ischemic stroke (within 24 hours of onset) who had been functionally independent before onset were prospectively enrolled in the present study. The poststroke BP levels were defined as the average values during the 48 hours after onset. The study outcomes were a good neurological recovery, neurological deterioration, and a poor functional outcome. The higher poststroke BP levels were significantly associated with a lower probability of a good neurological recovery and elevated risks of neurological deterioration and a poor functional outcome after adjusting for potential confounding factors. The multivariate-adjusted odds ratios (95% confidence interval) in the highest quintile of systolic BP (versus the lowest quintile as a reference) were 0.51 (0.37-0.71) for a good neurological recovery, 1.92 (1.15-3.27) for neurological deterioration, and 2.51 (1.69-3.74) for a poor functional outcome. Similar associations were observed when we applied the poststroke diastolic BP or pulse pressure. No evidence of the J-curve phenomenon was observed for each association. These results suggest that a high poststroke BP was significantly associated with unfavorable clinical outcomes in patients with acute ischemic stroke. There was no evidence of the J-curve phenomenon between the poststroke BP levels and the clinical outcomes.