Well-defined ultrathin nanotubes (30 nm in diameter and of micrometer-scale length) were generated through the self-assembly of a novel alternative copolymer synthesized using an epoxy–thiol click-chemistry reaction. The self-assembly mechanism was investigated both by experiments and using dissipative particle dynamics (DPD) simulations. The obtained nanotubes can be readily functionalized with carboxy groups, amino groups, peptides, or other groups by simple modular click copolymerization.