There is provided to a method for efficiently producing phosphonic acid metal salt fine particles with an average particle diameter of 0.5 μm or less with high efficiency. A method for producing phosphonic acid metal salt fine particles, comprising: a) causing a reaction of a phosphonic acid compound of Formula (I): (where R1 and R2 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkoxycarbonyl group having 1 to 10 carbon atoms) with a base in an aqueous medium to adjust a pH range of the reaction system to be neutral to basic; b) causing a reaction of the product obtained in a) with a metal salt to precipitate a phosphonic acid metal salt from the aqueous medium; c) removing water from the phosphonic acid metal salt precipitated in b); and d) heating and drying the phosphonic acid metal salt from which water is removed in c).