Arginine (Arg)-rich cell-penetrating peptides (CPPs) are promising tools for plasmid DNA (pDNA) delivery. α-Aminoisobutyric acid (Aib) is known to stabilize peptide helical secondary structures and has been used as a building block for foldamers. In the current study, we prepared Aib CPP foldamers, (Arg–Arg–Aib)_n (n = 1–6) and examined their pDNA transfection abilities. Transfection efficiencies of peptide/pDNA complexes are dependent on peptide chain length, with longer peptides (n ≥ 4) exhibiting better transfection abilities than an Arg nonapeptide. Furthermore, Aib CPP foldamers achieve prolonged transfection abilities compared with commercially available transfection reagents, which is probably because of the high resistance of the peptides to enzymatic degradation, thereby protecting the encapsulated pDNA for a long period. The obtained results demonstrated promising features of Aib CPP foldamers as pDNA delivery carriers.