The β-thymosins are a family of actin monomer-sequestering proteins widely distributed among vertebrate classes. The most abundant β-thymosins in mammalian species are thymosin β 4 (Tβ 4 ) and thymosin β 10 (Tβ 10 ), two small peptides (43 amino acids) sharing a high degree of sequence homology. In the present work, we have analyzed the distribution of Tβ 4 and Tβ 10 in the developing and adult rat cerebellum using in situ hybridization and immunohistochemistry techniques. Our results show that the temporal and cellular patterns of expression of both β-thymosins are different. In the young (7 and 18 postnatal days) and adult (1 and 4 months old) rat cerebellum, Tβ 4 was mainly expressed in the glia (microglia, Golgi epithelial cells and oligodendrocytes), neurons (granule cells and Purkinje cells), and in the capillaries. In 14-month-old rats, the Tβ 4 immunoreactivity was only detected in some microglia cells. In young and adult animals, most of the Tβ 10 immunoreactivity was localized in several types of neuronal cells including granule cells, Golgi neurons and Purkinje cells. In old animals, a faint Tβ 10 signal could be detected in a few Purkinje cells. Our results suggest that each β-thymosin could play a different function in the control of actin dynamics.