The effect of dispersant structures for dispersing single-walled carbon nanotubes (SWCNTs) is investigated. The monomer 3-hexylthiophene is used as the starting material for the development of a series of oligomers that are used to disperse SWCNTs in an organic solvent. The series is obtained by varying the number of head groups, the regioregularity of head groups, and the head-to-trail ratios of the hexyl group in the oligomers. The SWCNT solutions are characterised with UV-vis-near-IR spectroscopy and transmission electron microscopy. An increase in the number of head groups improves the dispersity of SWCNTs, and a regioregular oligomer plays an important role in dispersing SWCNTs. Furthermore, Raman spectroscopy and X-ray photoelectron spectroscopy shows that the sculfur atom head groups enhance interactions between the thiophenes and the SWCNT walls. The analysis demonstrated that a well-designed thiophene oligomer could afford well-dispersed SWCNT solutions with long-term dispersion stability even with an extremely low dispersant concentration.