We have previously reported that intravenous injection of l-citrulline, an α-amino acid isolated from watermelon juice, prevented the decrease in cerebral blood flow (CBF) during cortical spreading depression (CSD) in rats, a widely accepted animal model of migraine aura. However it is not clear whether oral l-citrulline administration improves CBF during CSD or not. For clinical application of l-citrulline against migraine aura, we evaluated the effect of oral l-citrulline administration on the parameters of CSD. Daily oral administration of l-citrulline for 8 consecutive days increased brain concentration of l-arginine as well as l-citrulline. Moreover, l-citrulline reduced the disturbance of CBF, monitored by laser Doppler flowmetry, with less effect on mean arterial pressure and heart rate during CSD. Although l-citrulline had no effect on CSD propagation velocity, it accelerated the recovery of CBF changes. These results suggest that l-citrulline has a clinically beneficial effect on migraine aura via regulation of CBF.