The entry of SARS-CoV-2 into host cells proceeds by a two-step proteolysis process, which involves the lysosomal peptidase cathepsin L. Inhibition of cathepsin L is therefore considered an effective method to prevent the virus internalization. Analysis from the perspective of structure-functionality elucidates that cathepsin L inhibitory proteins/peptides found in food share specific features: multiple disulfide crosslinks (buried in protein core), lack or low contents of α-helix structures (small helices), and high surface hydrophobicity. Lactoferrin can inhibit cathepsin L, but not cathepsins B and H. This selective inhibition might be useful in fine targeting of cathepsin L. Molecular docking indicated that only the carboxyl-terminal lobe of lactoferrin interacts with cathepsin L and that the active site cleft of cathepsin L is heavily superposed by lactoferrin. Food protein-derived peptides might also show cathepsin L inhibitory activity.