A process for producing a polyphenylene sulfide ketone polymer comprising reacting a dihalogen compound of the general formula ##STR1## wherein X and X', which may be the same or different, each represents a fluorine, chlorine, bromine or iodine atom, with an alkali metal sulfide in a polar solvent in such a way that the alkali metal sulfide is not deprived of free water or the water of hydration in the polar solvent before polymerization is started, and that the reaction is performed at a temperature in the range of from 80.degree. to 170.degree. C. in the initial period of polymerization until the percentage of residual unreacted dihalogen compound is reduced to 2% or below, with the subsequent reaction being performed at a temperature in the range of from 200.degree. to 345.degree. C.