The sulfidation-resistance value (S-W), proposed by R. Bartunek as an estimating method of reactivity of dissolving pulp, is the amounts of undissolved residue of pulp after emulsion xanthation at the definite concentration of sodium hydroxide solution, sufficient to mercerize cellulose, with 25% of carbon disulfide based on the pulp. The Bartunek's S-W shows only a point on the emulsion xanthation soluhility curve (S-W curve) as a function of the amount of carbon disulfide added. The significance of S-W curve and the relation between S-W curve and Bartunek's S-W must be investigated to make clear the significance of Bartunek's S-W as a estimating method of reactivity in dissolving pulp. In this paper, the relation between sulfidation and dissolution in S-W curve is examined, and an adequate expression method of characteristics of S-W curve is proposed.The results are as follows:1) S-W curve can be converted to the straight line on the following assumptions. a) Sulfidation and dissolution occur from the outer surface of fiber and advance to its center, namely fiber is peeled off gradually from the surface. b) If the amount of dissolved cellulose is expressed by the distance from the surface in radial direction (dissolved distance), the distance is proportional to the amount of carbon disulfide added in emulsion xanthation.2) The converted S-W curve (shown as calculated curve in Figs. 2, 3, 5 and 6) is consisted of three lines, and its inflexion-points correspond to the points at which distinctly γ-value of undissolved residue varies. This means that the reaction of pulp in emulsion xanthation is consisted of three steps of sulfidation and dissolution processes. In the last step, most of pulps show sulfidation-resistance.3) If sulfidation and dissolution of pulp advance on the assumption described above, the contents of S-W curve are as follows:When a ratio of the degree of sulfidation and dissolution is more uniform over the whole range of solubility on emulsion xanthation, the carbon disulfide is less consumed for the complete dissolution of pulp. How far to the fiber the sulfidation advance during emulsion xanthation, in comparison with the degree of dissolution (dissolved distance), determines the amount of carbon disulfide required for 100% dissolution of pulp, (1/A3) shown in Fig. 6.The ununiformity of converted S-W curve, (A2/A3-1) shown in Fig. 6, express the ununiformity of ratio of sulfidation and dissolution during emulsion xanthation process.4) From the above, S-W curve can be characterized by A3 and (A2/A3-1).