Stellate and basket cells in the molecular layer (ML) of the cerebellar cortex proliferate within the white matter (WH) during development. Developmental neuronal death has been documented on granule cells but has not been demonstrated on other GABAergic neurons. We investigated the migration and the cell death of stellate/basket cells further in glutamic acid decarboxylase 67/green fluorescent protein (GFP) knock-in mouse in which every GABAergic neuron was identified by its GFP fluorescence. Analyses were made in the first three postnatal weeks. In the WM, GFP-positive cells were abundant on postnatal day (P) 5-15 but scarce in P21. Stellate/basket cells increased in number in the ML until P15, corresponding to the growth of the ML. Administration of 5-bromo-2'deoxyuridine (BrdU) at P2-8 labeled many cells in the WM within 1h. After BrdU administration at P5, many BrdU-labeled GFP-positive cells were observed in the WM and the internal granular layer at P7, and in the ML at P9. These results support the proliferation of stellate/basket cells in the WM and their migration to the ML. Apoptosis of GABAergic interneurons was demonstrated in the ML and WM during the first two weeks. Their apoptotic loss will contribute to the adjustment of neuron number or elimination of any improper populations.