Abstract: Polyethylene glycol (PEG) of different lengths were prepared to investigate their effects on oral absorption of nanostructured lipid carrier (NLCs).Three kinds of PEG-modified NLCs with different chain lengths, including polyethylene glycol (100) monostearate (S100), polyethylene glycol (55) monostearate (S55), polyethylene glycol (40) monostearate (S40), were prepared by film dispersion method.Coumarin 6 was chosen as a fluorescent probe to characterize the physicochemical properties of NLCs with different lengths.Meanwhile, the stability of NLCs in simulate buffer, the release behavior, cytotoxicity of NLCs, the uptake kinetics and cellular uptake mechanisms were evaluated. This work demonstrated that the thickness of the hydrated layer increased with the increase of PEG length. Of note, S100-modified NLCs (pNLC-EG100) exhibited higher cellular uptake efficiency compared with other formulations. Thus, S100 was optimized as the best molecular weight for PEG-modified NLCs on oral drug delivery system.