Understanding the neurodevelopment of cerebellar nuclei (CN), the primary output of the cerebellum, is crucial. Traditionally, the rhombic lip (RL) and ventricular zone (VZ) have been known as the origins of glutamatergic excitatory and GABAergic inhibitory CN neurons, which emerge after embryonic day 9 (E9). However, our study uncovers a novel subset of cells in the nuclear transitory zone (NTZ), a transient area for future CN that appears even before E9. Our study’s objective is to map the fate of these early-appearing cells in the developing cerebellum. Utilizing SncaGFP transgenic mice, this study includes various techniques such as EdU (5-ethynyl-2'-deoxyuridine)-based birth-dating and migration analyses, immunofluorescence labeling, and confocal imaging. The findings showed that this early subset of cells in NTZ exhibit α-synuclein (SNCA) expression, which is encoded by the Snca gene. Birth-dating analysis indicated the emergence of these SNCA-positive cells in the NTZ as early as E8.5, which most probably originates from the mesencephalon as a potential germinal zone of these CN neurons. Additionally, colocalization of SNCA in these cells with glutamatergic markers hints at their nature as excitatory neurons. In conclusion, our study proposes that, in mice, an early subset of CN cells are glutamatergic neurons, which emerge at E8.5. Unraveling the origin and timeline of this early subset of CN neurons could significantly contribute to understanding various questions regarding neurodevelopmental disorders such as autism spectrum disorder (ASD).