Protein corona is immediately established on the surface of nanoparticles upon their introduction into biological milieu. Several studies have shown that the targeting efficiency of ligand-modified nanoparticles is attenuated or abolished owing to the protein adsorption. Here, transferrin receptor-targeting ligands, including LT7 (CHAIYPRH), DT7 (hrpyiahc, all d-form amino acids), and transferrin, were used to identify the influence of the ligand size and conformation on protein corona formation. The results showed that the targeting capacity of ligand-modified nanoparticles was lost after incubation with plasma in vitro, whereas it was partially retained after in vivo corona formation. Results from sodium dodecyl sulfate polyacrylamide gel electrophoresis and liquid chromatography-mass spectrometry revealed the difference in the composition of in vitro and in vivo corona, wherein the ligand size and conformation played a critical role. Differences were observed in cellular internalization and exocytosis profiles on the basis of the ligand and corona source.