Abstract: AimPoly (methoxypolyethyleneglycol cyanoacrylate-co-hexadecyl cyanoacrylate) (PEG-PHDCA) and PHDCA niosomes were prepared and the influence of the PEG chain length on the niosomes physicochemical characteristics, complement consumption and phagocytic uptake were studied. Methods The physicochemical parameters of PEG-PHDCA niosomes were characterized in terms of particle size, zeta potential, surface PEG density and fixed aqueous layer thickness. The relationship between physicochemical characteristics and in vitro complement consumption and phagocytic uptake was further illustrated. ResultsExperimental results showed that PEG_{10 000}-PHDCA had most loose structure and least PEG surface density among three groups. Configuration simulation through fixed aqueous layer thickness confirmed that PEG folding and less flexibility of the PEG chains of PEG_{10 000}-PHDCA niosomes were accountable for its poor stealth effects. Compared with PEG_{2 000}-PHDCA, PEG_{5 000}-PHDCA showed a thicker fixed aqueous layer (FALT) of 4.20 nm, less negative zeta potential of -10.03 mV, and enhanced PEG surface density of 0.49 PEG·nm^-2, leading to the best effects of reduction of complement consumption and phagocytic uptake. ConclusionExcessive chain length of PEG was not necessary for stealth effects of PEG-PHDCA niosomes. PEG_{5 000}-PHDCA niosomes had best effects on evading complement consumption and subsequent phagocytic uptake.