Method for producing chlorinated propylene-containing polymer

The present invention provides a method for producing a chlorinated propylene-containing polymer, said method comprising a step wherein a propylene-containing polymer is chlorinated in a mixed liquid of a chlorine-based solvent and water. This method is an improved production method by which an object product can be obtained more efficiently than conventional methods. The present invention specifically provides a method for producing a chlorinated propylene-containing polymer, which is characterized by comprising: (1) a step 1 wherein a dispersion liquid is obtained by dispersing at least one kind of propylene-containing polymer selected from among polypropylenes and propylene-alpha-olefin copolymers in a mixed liquid that contains chloroform and water; (2) a step 2 wherein the propylene-containing polymer is chlorinated by introducing a chlorine gas into the dispersion liquid, while heating the dispersion liquid at a temperature of 130 DEG C or less in a closed system; (3) a step 3 wherein a chloroform-conta