To provide a method for producing a polyketone, comprising copolymerizing carbon monoxide with an ethylenic unsaturated compound in the presence of a catalyst in a specific liquid medium, by which the polyketone having a high mol.wt. can be produced in a high yield.

This method for producing the polyketone, comprising copolymerizing the carbon monoxide with the ethylenic unsaturated compound in a liquid medium in the presence of an organic metal complex catalyst comprising (a) the compound of a transition metal in the group 9, 10 or 11 and (b) ligands each having an atom in the group 15 is characterized by using as the liquid medium a liquid medium which comprises water and water-soluble organic solvents and has a water concentration of 1 to 10,000 ppm, wherein the water concentration is represented by numerical expression (1): water concentration (ppm)=[water concentration (g)]/[volume (ml) of all water-soluble organic solvents + volume (ml) of water]×106 (1) (the volumes of the organic solvent and the water are values at 25°C, respectively). Thereby, the polyketone having a high mol.wt. and useful as an industrial material can be produced in a high yield in a short time and at a low cost.