An approach for tailoring self‐assembled tubular structures is described. By controlling the relative composition of a two‐component surfactant mixture comprising the natural bile salt lithocholate and its bolamphiphilic derivative, it was possible to finely tune the nanotube cross‐section of the mixed tubular aggregates that self‐associated spontaneously in aqueous solution at pH 12. The diameter was found to vary up to 50 % when the stoichiometric ratio of the two bile salts was changed. The tuning of supramolecular nanochannels with such remarkable precision is of significant interest for technological applications of these materials. The perfect fit: The tailoring of self‐assembled nanotube cross‐sections is described for two‐component mixtures of a bile acid and its derivative. By controlling the stoichiometry, diameters were found to vary by up to 50 %. Starting from pure tubules with a parallel arrangement of the monomer, a progressive inclusion of the second component in an antiparallel orientation is proposed to explain the variation in size.