Abstract: Carbon nanotubes have become a kind of superior antitumor drug and gene carrier due to their special cylindrical structure with high loading capacity and easy penetration into the cell membrane. With the gradual development of researches on carbon nanotubes, their applications in tumor photothermal therapy and diagnosis have also become current research hotspots. However, chemical inertness and aggregation of carbon nanotubes have limited their clinical application. To overcome their drawbacks, researchers would functionalize the carbon nanotubes before further researches. In this article, applications of functionalized carbon nanotubes in cancer chemotherapy and gene therapy, photothermal therapy and cancer diagnosis are summarized.