Fluoride ion removal by calcium fluoride crystallization was Studied. This study aimed to find the range of fluoride ion concentration which would be applicable to calcium fluoride crystallization. First, batch experiments without a seed crystal were conducted to obtain the relationship between initial fluoride ion concentration and calcium ion concentration where fluoride ion concentration would begin to decrease in the process of calcium fluoride precipitation. Batch experiments using a seed crystal were then conducted under the same conditions as those without a seed crystal to obtain the relationship between initial fluoride ion concentration and calcium ion concentration where fluoride ion concentration would begin to decrease due to crystallization of calcium fluoride on the seed crystal. Supersolubility curves of calcium fluoride were obtained from both sets of experiments. From these, the metastable region of calcium fluoride between the Solubility curve and the supersolubility curve was obtained. The range of fluoride ion concentration applicable to calcium fluoride crystallization was found to be less than 3 mmol/l. XRD of the grown calcium fluoride crystals was investigated. The main peaks of the calcium fluoride used in the experiments were found to agree with the literature values.