The fungal derived nitric oxide donors, (E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409) and N-[(E)-4-ethyl-3-[(Z)-hydroxyimino]-5-nitro-3-hexen-1-yl]-3-pyridinecarboxamide (FR144420), were evaluated for the treatment and prevention of cerebral vasospasm induced by subarachnoid hemorrhage (SAH) by an in vitro study using rabbit basilar artery. The tension-relaxation of a 3 mm-long artery segment was carried out in a micro-tissue organ bath with a real-time recorder to record the tension-relaxation curve. Steady contraction of the specimens was induced by KCI (n = 12) and oxyhemoglobin (oxyHb) (n = 12). Sodium nitroprusside was used for comparison. Each of the agents was added in ascending concentration. Relaxation caused by FK409 and FR144420 was significantly greater (p < 0.05) than that by sodium nitroprusside. Relaxation effects of FK409 and FR144420 on the KCl-induced steady contraction were better than those on the oxyHb-induced contraction. FK409 and FR144420 have potential uses for the treatment and prevention of SAH-induced cerebral vasospasm.