We report a mussel-inspired strategy of polydopamine (PDA) coating to stabilize and functionalize J-aggregate nanotubes (NTs) formed by supramolecular self-assembly of an amphiphilic cyanine dye called C8S3 in aqueous media. Optimization of the coating condition by changing the incubation time in a slightly basic media of dopamine with different concentrations leads to conformal wrapping of the PDA layer with controllable thickness on the surface of the NTs. Compared to noncoated pristine C8S3 NTs, these PDA-coated NTs show enhanced stability against dilution, heating, and photobleaching. Moreover, the PDA layer wrapping around the NTs serves as an adhesive for the adsorption of a variety of metal ions and electroless deposition of the metal nanoparticles. Such stabilized and functionalized NT composites may offer a robust synthetic J-aggregate system to mimic the structure and function of light-harvesting complexes and reaction centers in photosynthetic systems.