Inthispaperageneralformulaforplasticpotentialincludingisotropicductiledamagehasbeenpresentedonthebasisofthethermodynamicsforirreversibleprocessandinternalvariablethe-ory.Withthisformulathemassconservationlawissatisfiedanditalsocontainsaseriesofunknowcoefficientswhicharethefunctionofmacroequivalentstressandtheaveragemicroequivalentstressandanunknownfunctionwhichisthefunctionoftwogeneralizedforces.Theapproximateyieldsurfaceequationforisotropicallydamagedmaterialsisdeveloped.Usingthisequationthevoidgrowthrateiscalculatedfornonlinearmaterialcontainingvoids.Thepresentre-sultsareingoodagreementwiththenumericalresultsgivenbythecellmodel.