Many drugs have been delivered by different types of nanoscale vehicles to enhance their therapeutic efficacy. 5-Fluorouracil (5FU) is a widely used antitumor drug, however its bioavailability still needs to be improved. Herein we synthesized a polyethylene glycol monomethylether-C60–5FU conjugate (mPEG-C60–5FU) and evaluated its antitumor efficacy in vitro. The results show that the inhibition abilities of mPEG-C60–5FU to the human breast cancer cell line MCF-7 and the human gastric carcinoma cell line BGC-823 are significantly higher than that of 5FU. The conjugate has good stability in murine serum for at least 24 h. Moreover, the PEGylated fullerene (mPEG-C60) vehicle is non-toxic to MCF-7 cells. These results demonstrate that mPEG-C60 is an efficient vehicle for the delivery of 5FU.