The functionalization of GO nanomaterials with polyethylene glycol (PEG) polymers has been the most common method to ameliorate stability in physiological media and increase biocompatibility. In this work, carboxylated GO (CGO) was functionalized with PEG polymers of different molecular weight (MW) and structure and loaded with the anticancer drug paclitaxel (PCT). An increase in the MW of linear PEG from 2 to 20 kDA decreased the size and tended to increase the ζ-potential of the pegylated CGO nanoparticles (nCGO-PEG) and a branched (4 arm) PEG(10 kDa) provided nanoparticles with significantly lower size and higher ζ-potential compared to a linear PEG(10 kDa). All nCGO-PEG nanoparticle types exhibited good colloidal stability on storage and in PBS and cell culture medium with the exception of the nCGO-PEG functionalized with the relatively low MW PEG of 2 kDa. PCT loading efficiency fell when the MW of PEG was increased or a branched PEG was used. Pegylation decreased significantly the hemolytic potential of nCGO-PEG nanoparticles. Increased PCT release rate was observed at acidic pH 6.0 compared to physiological pH 7.4 for all PCT/nCGO-PEG formulations. Higher cytotoxicity and apoptotic activity of the nanocarrier-entrapped PCT compared to free PCT against the lung adenocarcinoma A549 cell line at longer incubation times was found as at these longer incubation times a high cellular uptake of the PCT/nCGO-PEG nanoparticles were observed. The results justify further investigation of the potential of PCT/nCGO-PEG as antitumor nanomedicine.