Abstract： Objective To investigate the effect of the fortified branch-chained amino acid (BCAA) and tyrosine (Tyr) on the monoamine in brain stem following motion stimulation. Methods Rats were fed with the compound preparation fortified with branch-chained amino acid and tyrosine for 10 days, and then contents of monoamine neurotransmitter in the rat brain stem were determined following motion stimulation. Results Following motion stimulation, norepinephrine (NE) and epinephrine (E) decreased, while 5-HT increased in the rat brain stem. When a comparison was made with the motion stimulation (MS) group, the content of NE in BCAA fortification group showed no significant change, whereas the content of E increased and 5-HT decreased. In the compound preparation group, the content of 5-HT was significantly lower, while NE and E were significantly higher than those of the MS group. Conclusions Preparation fortified with amino acids could influence changes in the contents of monoamine neurotransmitter in rat brain stem, which might be involved in the mental and physical functions of the animals during motion stimulation.