A series of peptide nucleic acid-oligo(bicycloguanidinium) (PNA-BGn) conjugates have been synthesized and characterized in terms of cellular antisense activity using the pLuc750HeLa cell splice correction assay. PNA-BG4 conjugates exhibit low micromolar antisense activity and the cellular activity requires the presence of the hydrophobic silyl terminal protecting group on the oligo(bicycloguanidinium) ligand and a minimum of four guanidinium units. Surprisingly a non-linear dose response with an activity threshold around 3-4 µM indicative of large cooperativity was observed. Supported by light scattering and electron microscopy analyses we propose that the activity and thus cellular delivery of these lipo-PNA-BG4 conjugates is dependent on self-assembled nano-aggregates. Finally, cellular activity is enhanced by the presence of serum. Therefore we conclude that the lipo-BG-PNA conjugates exhibit an unexpected mechanism for cell delivery and are of interest for further in vivo studies.