Poly(N-substituted glycine) "peptoids" are a class of peptidomimetic molecules receiving significant interest as engineered biomolecules. Sarcosine (i.e., poly(N-methyl glycine)) has the simplest side chain chemical structure of this family. In this Article, we demonstrate that surface-grafted polysarcosine (PSAR) brushes exhibit excellent resistance to nonspecific protein adsorption and cell attachment. Polysarcosine was coupled to a mussel adhesive protein-inspired DOPA-Lys pentapeptide, which enabled solution grafting and control of the surface chain density of the PSAR brushes. Protein adsorption was found to decrease monotonically with increasing grafted chain densities, and protein adsorption could be completely inhibited above certain critical chain densities specific to different polysarcosine chain lengths. The dependence of protein adsorption on chain length and density was also investigated by a molecular theory. PSAR brushes at high chain length and density were shown to resist fibroblast cell attachment over a 7 week period, as well as resist the attachment of some clinically relevant bacterial strains. The excellent antifouling performance of PSAR may be related to the highly hydrophilic character of polysarcosine, which was evident from high-pressure liquid chromatography measurements of polysarcosine and water contact angle measurements of the PSAR brushes. Peptoids have been shown to resist proteolytic degradation, and polysarcosine could be produced in large quantities by N-carboxy anhydride polymerization. In summary, surface-grafted polysarcosine peptoid brushes hold great promise for antifouling applications.