Amphiphilic lipid-poly(ethylene glycol) (LPEG) is widely used for the noncovalent functionalization of graphene nanomaterials (GNMs) to improve their dispersion in aqueous solutions for biomedical applications. However, not much is known about the detachment of LPEGs from GNMs and macrophage uptake of dispersed GNMs in relation to the alkyl chain coverage, the PEG coverage, and the linker group in LPEGs. In this study, we examined these relationships by using single-walled carbon nanohorns (SWCNHs). The high coverage of PEG rather than that of alkyl chain dominantly suppressed the detachment of LPEGs from SWCNHs in the protein-contained physiological solution. Correspondingly, the macrophage uptake quantity of LPEG-covered SWCNHs (LPEG-SWCNHs) decreased at a high PEG coverage. Our study also demonstrated the effect of ionic group in LPEG on the SWCNHs uptake into the macrophage cells. A phosphate anionic group in LPEG induced lower alkyl chain coverage and easy detachment of LPEG, however, the negative surface charge of LPEG-SWCNHs reduced the uptake of SWCNHs by macrophage cells.