Poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) was grafted onto cotton fabric by surface-initiated atom transfer radical polymerization (SI-ATRP). The wettability of the as-prepared cotton fabric surface can reversibly switch between superhydrophobic (154°) and superhydrophilic (< 5°) by exchanging the counterions between perfluorooctanoate anion (PFO) and SCN⁻, respectively. The effect of solvent on the counterion exchange was investigated, and we found that water was a poor solvent for counterion exchange, while other solvent systems, such as water/methanol, methanol and acetone, were good solvents for counterion exchange in this study. Moreover, the effect of the anions on the wettability of the PMETAC films was also studied. The as-prepared cotton fabric with controllable wettability may find application in soft superhydrophobic materials and multifunctional textiles.