To study the histological changes of cerebellar cortex of immature Red-billed Leiothrix(Leiothrix lutea) at different days of age, brains were sampled from Red-billed Leiothrixs at 1, 5 and 9 days of age. Through H.E. and toluidine blue staining, the coronal section of the cerebellum was observed to analyze the changes of cellular and postnatal structural patterns by microscope, and all the data were dealed with one-way ANCOVA. The results are as follow：The H.E. staining shows that the cerebellar cortex of Red-billed Leiothrix at 1 day of age consisted of three layers, namely external granular layer (EGL), unclear Purkinje cell layer (PCL) and internal granular layer (IGL), the external granular layer was obvious, but the margin of Purkinje cell layer and internal granular layer was not distinct (Fig1a, 1d). At 5 and 9 days of age, a clear four-layer structure was observed, including external granular layer, molecular layer (ML), Purkinje cell layer and internal granular layer (IGL)(Fig1b ~ 1c, 1e ~ 1f). With the increase of the age, the thickness of the cortex, molecular layer and internal granular layer were significantly increased (P < 0.01). Toluidine blue staining shows clearly that the size of Purkinje cell was significantly increased with the increase of the age. At 1 day of age, the Purkinje cell was small with pyriform and the nissl body was dark-colored(Fig2a, 2d), at 5 days of age, the Purkinje cells were enlarged(Fig2b, 2e). At 9 days of age, the size of the Purkinje cell was increased and the boundary between Purkinje cell layer and internal granular layer was apparent (Fig2c, 2f). Although the thickness of external granular layer thins after a slightly increase and has no significant change (P > 0.05) (Table 1), there was a reduced proportion of the external granular layer to the cortex(Table 2). Also the index of internal granular layer to the cortex was increased(Table 2). The results showed that the histological structure of cerebellar cortex was gradually matured in Red-billed Leiothrixs after early hatching. The changes of external granular layer and internal granular layer suggested that the granular cells in internal granular layer might migrate from external granular layer.