Disclosed herein are a melt-stable poly(arylene thioether-ketone) having predominant recurring units of the formula ##STR1## and having a melting point, Tm of 310.degree.-380.degree. C., a residual melt crystallization enthalpy, .DELTA.Hmc (420.degree. C./10 min) of at least 10 J/g, a melt crystallization temperature, Tmc (420.degree. C./10 min) of at least 210.degree. C., and a reduced viscosity of 0.2-2 dl/g as measured at 25.degree. C. and a polymer concentration of 0.5 g/dl in 98 wt. % sulfuric acid as well as a production process of the poly(arylene thioether-ketone). The poly(arylene thioether-ketone) has melt stability so that conventional melt processing techniques can be applied easily. The poly(arylene thioether-ketone) is a highly-crystalline polymer whose density is at least 1.34 g/cm.sup.3 when annealed at 280.degree. C. for 30 minutes.