The amygdala is located in the caudal part of the ventral telencephalon. It is composed of many subdivisions and is involved in the control of emotion. It is important to know the mechanisms of amygdalar development in order to analyze the pathogenesis of emotional disorders, but they are still not adequately understood. In the present study the migration, differentiation, and distribution of amygdalar neurons in the mouse embryo were investigated by means of in utero electroporation. Ventricular zone cells in restricted regions, that is, the caudal ganglionic eminence (CGE), the ventral pallium, the lateral pallium, and the diencephalon, were labeled with an expression vector of the enhanced green fluorescent protein (EGFP) gene. Labeling at embryonic day (E)10 revealed that the central nucleus originates from the neuroepithelium in the ganglionic eminence and the labeling at E11 and E12 revealed that the basolateral complex originates from the neuroepithelium of the ventral and lateral pallia. The introduction of the EGFP gene into the neuroepithelium of the third ventricle at E11 showed that the medial nucleus originates, at least in part, from the neuroepithelium of the diencephalon and migrates over the diencephalo-telencephalic boundary. The radial glial arrangement corresponded well with the initial migration of amygdalar neurons, and the radial processes later formed the boundary demarcating the basolateral complex. These findings indicate that the neurons originating from the temporally and spatially restricted neuroepithelium in both the telencephalon and diencephalon migrate and differentiate to form the mosaic of amygdalar subdivisions.