We investigated the neuritogenic effects of Tremella fuciformis (TF), which has been valued in traditional Chinese medicine as a remedy with nutritive and tonic actions, on PC12h cells. The cognitive improving effects of TF on scopolamine-induced (2 mg/kg, s.c.) amnesia in rats were also evaluated with using the Morris water maze task and by performing choline acetyltransferase (ChAT) immunohistochemistry. The water extract of TF (0.01-1 microg/ml) promoted neurite outgrowth of the PC12h cells in a dose dependent manner. TF was highly efficient at the concentration range of 0.1-1 microg/ml. Oral daily treatment with TF (100 or 400 mg/kg) for 14 consecutive days significantly reversed the scopolamine-induced deficit in learning and memory, and it alleviated decrease in cholinergic immunoreactivity induced by scopolamine in the medial septum and hippocampus. The results demonstrate that the promotion of neuritogenesis in neuronal culture cells by TF water extract is related with its activity for improving the performance of rats on a spatial learning and memory task. Moreover, the impairments of spatial learning and memory may be attributable to the decrease in activation of the septohippocampal cholinergic system and that TF ameliorated learning and memory deficits partly through its increasing the central cholinergic activity. Therefore, TF could represent a potentially useful agent that is able to improve the function of impaired cognitive processes.