The a-helical second generation peptide dendrimer of sequence (AcAMEA)(4)(KKLME)(2)KMKLA is more stable than the corresponding linear peptide AcAMEAAKLMEAMKLA toward pH-induced unfolding and temperature-induced intermolecular aggregation. The effect is interpreted in terms of an a-helix spanning across two successive branching points of the dendrimer. This stabilization effect is unprecedented and opens the way to folded dendritic analogues of proteins using natural amino acids only.