Peptides perform a wide variety of essential functions in living organisms with great specificity and precision. However, their therapeutic use is limited, due to their fast degradation by proteases in vivo and consequent poor oral bioavailability. Thanks to their proteolytic resistance and easily accessible and derivatizable synthesis on solid supports, peptoids (N-substituted glycine oligomers) have emerged as promising peptidomimetics for biological and medical applications. In this work peptoid analogs of two short amino acid sequences with antitumor activity (one derived from the CD44-v6 coreceptor and one from the BAG-1L protein), have been designed and synthesized. Comparison of the biological activity of the peptides and the different peptoid analogs led to the establishment of structure-activity relationships and the identification of a lead compound showing high potential for cancer therapy. In addition, a method for the synthesis of amide-containing submonomers as free bases and their incorporation into peptoid oligomers is described. Different-length homo-oligomers of α-chiral amide residues were successfully synthesized for structural investigations.