To provide agents for treatment of fluorine-containing wastewater and a method for treatment of fluorine-containing wastewater which can remove fluorine efficiently from fluorine-containing wastewater in a simple way and at a low cost.

This invention comprises an agent for treatment of fluorine- containing wastewater characterized by consisting of (A) a solution containing aluminum ions and carbonate ions and (B) a magnesium salt. This invention also relates to a method for treatment of fluorine-containing wastewater characterized by including a process for removing fluorine from wastewater based on a double salt formation process by the addition of the components A and B below to the fluorine-containing wastewater to let them react to form double salts. The addition amount of the agent A is desirable to be 10-1000 m ppm in terms of aluminum content.