Accumulations of β‐amyloid protein are characteristic and diagnostic features of the brain of Alzheimer's disease patients; however, the physiological role of this protein in CNS is unknown. We have previously reported that continuous infusion of β‐amyloid protein into rat cerebral ventricle impairs learning ability and decreases choline acetyltransferase activity, a marker enzyme of cholinergic neuron. In this study, the effects of β‐amyloid protein infusion on the release of neurotransmitters in cholinergic and dopaminergic neuronal systems were investigated by using an in vivo brain microdialysis method. Nicotine‐stimulated release of acetylcholine and dopamine in these animals was significantly lower than that in vehicle‐infused rats. Further, dopamine release induced by high‐K stimulation was decreased in β‐amyloid protein‐infused rats compared with vehicle‐infused rats. These results suggest that the release of the two transmitters, acetylcholine and dopamine, was decreased by β‐amyloid protein and that learning deficits observed in the β‐amyloid protein‐infused rats are partly due to the impairment of neurotransmitter release. Furthermore, continuous infusion of β‐amyloid protein may be a useful method to produce the animal model of Alzheimer's disease.