1. Icariin is a major constituent of flavonoids derived from the Chinese medicinal herb Epimedium revicornum Maxim. The aim of the present study was to investigate whether icariin has protective effects on learning ability and memory in a rat model of chronic cerebral hypoperfusion. 2. Chronic cerebral hypoperfusion was induced by permanent ligation of the common carotid artery in Wistar rats for 4 months. One month after permanent artery occlusion, rats were adminitered icariin at doses of 0, 30, 60 or 120 mg/kg per day, p.o., for 3 months. Neurobehavioural and neurobiochemical parameters were examined to evaluate the effects of icariin on cognitive deficits induced by chronic cerebral hypoperfusion. 3. The Morris water maze test revealed that learning ability and memory were severely impaired in untreated rats, but were significantly improved in icariin-treated rats. Icariin treatment also ameliorated chronic cerebral hypoperfusion-induced oxidative stress in the brain, as evidenced by reduced malondialdehyde formation and maintained superoxide dismutase activity. In addition, the decreased hippocampal levels of acetylcholine, acetylcholinesterase and choline acetyltransferase associated with chronic cerebral hypoperfusion were significantly prevented by icariin treatment. 4. In conclusion, icariin protects against cognitive deficits induced by chronic cerebral hypoperfusion in rats. These effects appear to be mediated through its anti-oxidant effects, as well as its effects on the circulatory and cholinergic systems.