ABSTRACTWe report the effect of wet ball‐milling process under mild neutral salt conditions on the alteration of crystallinity and surface state of microcrystalline cellulose (MC). The ball‐milling experiments were performed when the MC was immersed in H2O, NaCl aqueous solution, and KCl aqueous solution. Two collation groups, i.e., MC immersed in H2O2 and nonimmersed MC were additionally investigated for comparison. Except when H2O2 was present, the highest decrease in the cellulose crystallinity index (CI) was observed in dilute KCl. On the other hand, the CI of wet‐milled MC/NaCl was greater than that of the wet‐milled MC/H2O, however, still lower than that of the non‐immersed MC. XPS results showed that the carbonization progressed in dry‐milled MC and wet‐milled MC/NaCl surfaces. Though, the surface oxidization progressed in wet‐milled MC/H2O and wet‐milled MC/KCl. Lastly, the ball‐milling processes in different solutions led to various decreases of the crystallinity and the surface degradation due to carbonization and/or oxidization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44903.