The present investigation was carried on the cerebellum of 16 dog foetuses of both sexes ranging from 10 to 200 mm CVR length. In addition, the cerebellum of 10 dogs representing the suckling period (0-45 days old) was also studied. In dog embryos ranging from 10 to 15 mm CVR length, the dorsolateral parts of the alar plates of the metencephalon bent medially and formed the rhombic lips, the primordium of cerebellum. At 50-60 mm CVR length, as a result of increasing pontine flexure, the cerebellar plate was formed by the fusion of the rhombic lips. This cerebellar plate was differentiated into 4 distinct layers, a neuroepithelial, a mantle; a molecular and an external granular layer. On reaching 100 mm CVR length, the cerebellar surface showed the beginning of fissuring as well as the internal granular layer became clearly demarcated from the mantle layer which increased with the advancement of age. The external granular layer reached its maximum thickness at 50-60 mm CVR length dog foetuses, then it decreased with the advancement of age until it disappeared in most areas of cerebellar cortex in the postnatal 45 days old dog. On the other hand, the molecular and internal granular layers increased in thickness on the expense of the external granular layer. The Purkinje cell layer was formed of 3-4 cells in thickness in 140 mm CVR length dog foetuses, where it was disposed into a single row of cells at 25 days old. Toward 45 days old, the Purkinje cells increased in size and attained their full mature structure. The latter age showed that the cerebellar cortex had 3 distinct layers; an outer molecular layer, a central layer of Purkinje cells and inner granular layer, the characteristic features of the adult form.