Provided is a method for producing a lithium metal phosphate, and the method comprises initiating and allowing to proceed, in the presence of a polar solvent, a conversion reaction of a lithium ion (Li+) source such as lithium hydroxide, a divalent transition metal ion (M2+) source such as a divalent transition metal sulfate, and a phosphate ion (PO43−) source such as phosphoric acid into a lithium metal phosphate at 150° C. or higher. The conversion reaction is initiated and allowed to proceed by bringing solution A containing one of a lithium ion, a divalent transition metal ion, and a phosphate ion into contact with solution B containing the others of these ions at 150° C. or higher, or by adjusting the pH of solution C that has a pH of lower than 4 and contains a lithium ion, a divalent transition metal ion, and a phosphate ion to 4 or higher.