The ROR alpha is a member of the nuclear hormone receptor gene superfamily, and its deletion causes the staggerer mutation in mice. In the staggerer mutant mouse, Purkinje cells (PCs) are severely affected in the cytology, synapse formation and gene expression. We previously found the presence of mediolateral compartments unique to the staggerer cerebellum, based on different degrees of abnormalities in the cytology and gene expression. In this paper we investigated expression of the ROR alpha mRNA in developing mouse cerebellum, with a particular interest in its regional difference. At embryonic day 15, the ROR alpha mRNA was expressed at the highest level in the PC plate. The prominent expression in PCs was maintained from late embryonic stage through mature stage. At any developmental stages, no apparent regional differences in the ROR alpha mRNA expression were detected in the mediolateral and rostrocaudal axes of the cerebellum. The high expression from early developmental stages provides a molecular-anatomical basis for its important role in phenotypic differentiation of PCs. However, the even distribution in the cerebellum suggests that the unique staggerer compartments are not directly related to the loss of ROR alpha function.