A turn-on fluorescein-based probe (1) has been successfully developed for the highly sensitive and selective detection of sulfite. The probe exhibits high SO₃²⁻ selectivity over other common anions and biothiols (Cys, Hcy and GSH), and the detection limit was measured to be 0.55 μM. Probe 1 exhibited high selectivity towards SO₃²⁻ with a broad pH (4–9). A significant change from colorless to yellow could be directly observed by the naked eye. Furthermore, living cell imaging results demonstrated its practical application value in biological systems.