Aluminosilicate nanotubes (AlSiNTs), a nontoxic clay material with single-walled structure and high aspect ratio, represent a promising inorganic material for fabricating composite thin films and membranes for low-k and biotechnological applications. Their fair dispersion in aqueous media and, in particular, optical transparency allow for the use of optical characterization schemes (e.g., light scattering and rheo-optics) to delve into the structural features and true dispersion state in addition to the usually reported rheological properties. Previous studies have revealed excellent dispersion and electrospinning properties of AlSiNT/PVA aqueous dispersions. In this work, to help solve water-absorption problem in AlSiNT-based thin films that can notably weaken the low-k properties, the interior wall of AlSiNTs is modified with methyl group, thus promoting the hydrophobicity of AlSiNTs. The dispersion properties of the functionalized AlSiNTs (i.e., CH3-AlSiNTs) are observed to differ substantially from those of the unmodified counterpart. Among them, pure (1 wt%) CH3-AlSiNT suspension is noted to exhibit strong thixotropic behavior, previously unobserved with the unmodified-AlSiNT suspensions. The resulting CH3-AlSiNT/PVA dispersions, whose structural and rheological properties are under systematic exploration, are expected to serve as a highly versatile material for current nanotechnological applications.