There is provided a method of end-chlorination of a fluorine-containing compound which can easily provide a fluorine-containing monomer having a functional group such as nitrile group at relatively low cost. The method of chlorinating an end of a fluorine-containing compound having iodine atom at an end thereof comprises reacting a fluorine-containing organic compound having iodine atom at a molecular end thereof and represented by the formula (I): RfCX.sub.2 I (I) wherein Rf is an organic residue having fluorine atom, X is hydrogen atom or chlorine atom, with a chlorine gas at a temperature of from 150.degree. C. to 180.degree. C. under irradiation with light to cleave the C--I bond and replace iodine atom with chlorine atom.