Apodemus agrarius has been used for experimental purpose to identify the route of infection and pathogenesis of Korean hemorrhagic fever. However, despite the increasing amount of information being published at present about the physiologic and ecologic characteristics of Apodemus, few data are available about the morphologic findings in the brain. This study was aimed to clarify the change of NADPH-d and neuropeptide Y (NPY) associated with aging of the Apodemus. The number of NADPH-d positive or negative NPY neurons in the cerebral cortex and striatum were compared between two age groups of Apodemus (4 months and 24 months) after the histochemical and immunohis-tochemical staining. 1. The number of NADPH-d positive NPY neurons in cerebral cortex or striatum were not different between the two age groups. 2. The number of NADPH-d negative NPY neurons in cerebral region or caudatoputamen striatum were not different between the two age groups. 3. Most of NADPH-d or NPY neurons were bipolar or multipolar neurons with complex and long dendrites in the control group. 4. The NADPH-d or NPY neurons in cerebral cortex were more tortous and shorter than control in the aged group. These findings demonstrate that NADPH-d positive NPY neurons and NPY neurons do not seem to be change of age in cerebral cortex or striatum of Apodemus agrarius.