Bisthiocarbonohydrazones are found to be a class of sensitive, selective, ratiometric, and colorimetric chemosensors for anions such as fluoride (F-) or acetate (Ac-). The sensitivities, or the binding constants of the sensors with anions, were found to be strongly dependent on the substituents appended on the π-conjugation framework, the delocalization bridge CH=N, the aromatic moiety, and the hetero atom in the C=X group (X=O, S) of the sensors. Single-crystal structures and 1H NMR titration analysis shows that the CH=N moiety is a hydrogen- bond donor, and it is proposed that an additional CH…F hydrogen bond is formed for the sensors in the presence F-1. A sensor bearing anthracenyl groups is demonstrated as a switch-on fluorescent chemosensor for F-1 and Ac-1. The recognition of F-1 in acetonitrile (MeCN) by a sensor with nitrophenyl substituents is tolerant to MeOH (MeCN/MeOH=10:1, v/v) and water (MeCN/H2O=30:1, v/v); at these solvent ratios the absorption intensity of the sensor-F-1 complex solution at maximal absorption wavelength was attenuated to half of the original value in pure MeCN.