Paclitaxel (PTX) is an extensively used potent chemotherapy drug; however, low water solubility, poor bioavailability, and emergence of drug resistance in patients limited its biological application. In this report, we proposed a new drug delivery system for cancer therapy based on graphene oxide (GO), a novel 2D nanomaterial obtained from the oxidation of natural graphite, to improve the utilization rate of PTX. PTX was first connected to biocompatible 6-armed poly(ethylene glycol), followed by covalent introduction into the surface of GO sheets via a facile amidation process under mild conditions, affording the drug delivery system, GO-PEG-PTX (size 50200 nm). GO-PEG nanosized carrier could quickly enter into human lung cancer A549 and human breast cancer MCF-7 cells verified by inverted fluorescence microscope using fluorescein isothiocyanate as probe. This nanocarrier was nontoxic to A549 and MCF-7 cells without linking with PTX. Nevertheless, GO-PEG-PTX showed remarkably high cytotoxicity to A549 and MCF-7 cells in a broad range of concentration of PTX and time compared to free PTX. This kind of nanoscale drug delivery system based on PEGylated GO may find widespread application in biomedicine.