As a breakthrough to the traditional ¹H diffusometry, the interaction of cations with cellulose is investigated via⁷Li and ²³Na PFG-SE NMR. The diffusion coefficient of Li⁺ decreases more than that of Na⁺ with the addition of cellulose, which indicates a stronger binding of LiOH with the macromolecule. Therefore, a new, facile, accurate and repeatable method to characterize ion/polymer interactions is established.