The effects of (-)clausenamide (claus) on brain development were studied. Sixty kunming strain weaning mice were divided into 4 groups. One group was served as control administered with normal saline, the other 3 groups were treated with (-)claus 5, 10 and 20mg kg−1respectively by gavage once a day for 4 weeks. Results showed that (-)claus at dosage of 5 and 10 mg kg−1facilitated learning and memory acquisition in step down and step through tests and increased thickness of cerebral cortex and synapse density significantly in the dentate cells over pyramidel cells in hippocampal region using quantitative technique of synapses analysis. These data provided the morphological basis of the nootropic effect of (-)claus.