L-Theanine (LTE) is a derivative of glutamic acid, which is abundant in tea leaves and contributes to the umami and sweetness of tea. In recent years, its effects on the brain, such as relaxation, have been attracting attention. In this study, we used imaging mass spectrometry (IMS) to visually analyze the changes in the catecholamine system in the brain after the administration of LTE. In IMS, we applied derivatization reagent to improve detection limit. Simultaneous imaging of catecholamines, LTE and g-aminobutyric acid (GABA) is particularly useful to understand a metabolic pathway. We investigated whether symptom of depression is improved or not by free drinking of LTE water. The mice that are freely drinking of theanine (Group 1), symptoms of depression was milder than that of drinking of water (Group 2). IMS showed dopamine (DA) marginally produced from caudate putamen from Group 2, but DA was produced from the Group 1. Interestingly, GABA increased at hypothalamus nucleus paraventricularis (PVN), which controls eating amount, from Group 1 compared with Group 2. We hypothesized an increasing of GABA at PVN works an appetite stimulation. Practically, an appetite of mouse in Group 1 was not decreased compared with that in Group 2. IMS visually gives us the pathway of catechol amine and improvement of depression by theanine.