Estradiol-peptidomimetic conjugates (EPCs) are linear, sequence-specific peptoid oligomers that site-specifically display multiple copies of 17β-estradiol (E2), a ligand for the human estrogen receptor α (hERα). We evaluate the ability of multivalent EPCs to activate hERα-mediated transcription. EPCs activated the hERα in both a length- and valence-dependent manner, with the highest levels of activation generated by divalent peptoid 6-mers, divalent 18-mers, and trivalent 9-mers. Hexavalent EPCs did not activate hERα, but instead blocked E2-mediated hERα activation. The physicochemical features of EPCs can be precisely tuned, which may allow the generation of a library of chemical tools for modulating specific effects of estrogens.