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Fluorinated In(OH)ySzsolid solutions were synthesized via a hydrothermal method. The photocatalytic degradation of rhodamine B (RhB) over the fluorinated In(OH)ySzsolid solutions revealed that the process of the de-ethylation of RhB was enhanced, while in the meantime, the rate of the mineralization of RhB was suppressed when In(OH)ySzwas fluorinated. To elucidate the opposite effects of fluorination on the two processes of photocatalytic degradation of RhB (de-ethylation and mineralization) over In(OH)ySz, the adsorption of RhB over In(OH)ySzwith and without fluorination, the active species involved in the de-ethylation and the mineralization of RhB, were investigated, and the electronic structure of fluorinated In(OH)ySzwas studied. The results indicated that the major active species involved in the de-ethylation and the mineralization of RhB are different, that is, the hole direct oxidation leads to the de-ethylation of RhB, while the major active species responsible for the mineralization of RhB is the O2−•radical. The fluorination on In(OH)ySzsolid solutions on one hand can enhance the adsorption of RhB on the catalyst surface, leading to a higher rate in the de-ethylation of RhB. On the other hand, fluorination lowers the conduction band of In(OH)ySz, which leads to a lower capability of the photogenerated electrons in the reduction of O2to give O2−•radicals. Our results clearly show that the fluorine modifications can have ambilateral effects on the photocatalytic performance of semiconductor photocatalysts depending on the specific photocatalytic reactions.