Patients with subarachnoid hemorrhage (SAH) who later suffer hydrocephalus show persistently high levels of transforming growth factor-β1 (TGF-β1) in the cerebrospinal fluid after the onset of SAH. Recombinant TGF-β1 induces hydrocephalus in mice. This study examined the spatial learning ability of rats after intraventricular administration of TGF-β1. Thirteen-week-old Wistar rats were treated with 0.8 or 8.0 μg of human recombinant TGF-β1 by direct injection or via osmotic pump. Three months later, their spatial learning ability was evaluated with a Morris water maze. Ventricular size, ultrastructural features, and sodium-potassium-adenosine triphosphatase (Na⁺,K⁺-ATPase) activity of the subarachnoid space were examined. All three TGF-β1-treated groups clearly exhibited impaired spatial learning ability, but they did not exhibit ventricular dilation. Histological examination revealed subarachnoid fibrosis and deactivation of Na⁺,K⁺-ATPase in the arachnoid cells. These findings are similar to those of our previous experiments involving injection of TGF-β1 in mice. The present and previous studies suggest that subarachnoid fibrosis is an important factor in the disturbance of the spatial learning ability of rats, whereas ventricular size is less important.