The present invention is a polyether-based polymer composition includes: a polyether-based polymer including an oxirane monomer unit and having one cationic group substantially only at one terminal of a polymer chain, and a nanocarbon material. The polyether-based polymer composition of the present invention can be suitably used, for example, as a bucky gel or as a master batch for preparing a nanocarbon material aqueous dispersion in which a nanocarbon material is favorably dispersed.