The pre-T cell receptor (TCR) is crucial for early T cell development and is proposed to function in a ligand-independent way. However, the molecular mechanism underlying the autonomous signals remains elusive. Here we show that the pre-TCR complex spontaneously formed oligomers. Specific charged residues in the extracellular domain of the pre-TCR alpha-chain mediated formation of the oligomers in vitro. Alteration of these residues eliminated the ability of the pre-TCR alpha-chain to support pre-TCR signaling in vivo. Dimerization but not raft localization of CD3epsilon was sufficient to simulate pre-TCR function and promote beta-selection. These results suggest that the pre-TCR complex can deliver its signal autonomously through oligomerization of the pre-TCR alpha-chain mediated by charged residues.