Thymosin Alpha-1 is a synthetic 28-amino-acid acetylated peptide originally isolated from thymic tissue, and a member of the thymic peptide class. It carries an acetylated N-terminus and is the same sequence whether produced by synthesis or derived from thymosin fraction five.

In the published preclinical literature, Thymosin Alpha-1 has been characterised at the cellular and molecular level for how it engages Toll-like receptor signalling on myeloid cells, with cultured and animal-model work mapping its association with dendritic-cell surface-marker expression and with intracellular kinase cascades such as the mitogen-activated protein kinase pathway. It is supplied as a research compound and is not intended for human or veterinary use.