Aim: Functional analyses of water-dispersed carbon nanohorns with antitumor activity were performed to explore their potential as a drug carrier for local cancer chemotherapy. Materials & methods: Water-dispersed carbon nanohorns were prepared through adsorption of polyethylene glycol-doxorubicin conjugate (PEG-DXR) onto oxidized single-wall carbon nanohorns (oxSWNHs). PEG-DXR-bound oxSWNHs were administered intratumorally to human nonsmall cell lung cancer-cell NCI-H460-bearing mice. Results & discussion: When injected intratumorally, PEG-DXR-bound oxSWNHs caused significant retardation of tumor growth associated with prolonged DXR retention in the tumor. In accordance with this DXR retention, a large number of oxSWNH agglomerates was found in the periphery of the tumor. Histological analyses showed migration of oxSWNHs to the axillary lymph node, which is a major site of breast cancer metastasis near the tumor, possibly by means of interstitial lymphatic-fluid transport. Conclusions: These results suggest that water-dispersed oxSWNHs may thus be useful as a drug carrier for local chemotherapy.