Given their large surface area and versatile chemical reactivity, single-walled carbon nanotubes (SWCNTs) are regarded as the basis of new pharmacological complexes. In this study, SWCNTs are chemically functionalized with fluorescein, folic acid, and capecitabine, a drug that is commonly used against colorectal cancer. These functionalized SWCNTs are dispersed in water by taking advantage of their synergistic interaction with type-II nanocrystalline cellulose (II-NCC), and the resulting colloidal system is tested in vitro on both normal (differentiated) and cancerous (proliferative) human colon cells (Caco-2). The functionalized SWCNT/II-NCC hybrids show a higher activity than the reference (capecitabine) against the Caco-2 cancer cell line. However, this effect appears to be intrinsically associated with the SWCNT/II-NCC complex, particularly boosted by fluorescein, as the presence of capecitabine is not required. In addition, confocal microscopy fluorescence imaging using cell cultures highlights the enormous potential of this nanohybrid platform for colon cancer theranostics. Display omitted •A nanohybrid material made of comprising carbon nanotubes and nanocellulose has been explored studied.•The sSurface functionalization of nanotubes turns converts it this material into a theranostic platform.•In vitro tests with human colon cells (normal and cancer behaviours types) were conducted.•Only the nanohybrid with type-II nanocellulose selectively kills colon cancer cells.•The sSurface attachment of a chemotherapy drug has no additional therapeutic effects.