To obtain an oily ink which is used for electrostatic type ink jets, has excellent ink extrusion stability and excellent brilliant image-forming property, gives images having excellent strengths, and enables the formation of printing plates that can form many printed products having brilliant images.

This oily ink for electrostatic ink jet is obtained by dispersing copolymer resin particles in a non-aqueous carrier liquid having an electric resistance of ≥109 Ω.cm and a dielectric constant of ≤3.5. The copolymer resin particles are obtained by subjecting a solution containing (A) a monofunctional monomer which is soluble in non-aqueous solvents but can be polymerized into a polymer insoluble in the solvents, (B) a monofunctional monomer which contains an amino group and can be copolymerized with the monomer (A), (C) a monofunctional monomer which contains a SO3H group and/or a SO2H group and can be copolymerized with the monomer (A), (MA) a monofunctional macromonomer in which a polymerizable double bond group is bound to only one end of the main chain of a polymer containing specific structure repeating units, and (P) a dispersion-stabilizing resin which contains a component for solubilizing the resin in a dispersing solvent, to a copolymerizing and particularizing treatment.