The dyeing properties of Argon (Ar)-plasma treated wool were studied using the six classes of dyestuffs, i.e., acid, acid metal complex, acid mordant, reactive, basic and disperse dyes. Ar-plasma treatment greatly improved the color yield and levelness, together with the decrease of tippy dyeing. A condition in the plasma treatment enhanced not only the color yield but also the anti-felting performance, which is due to high hydrophilic effect. The relationship between the improvement of dyeing properties by the plasma treatment and the chemical structure of the dyes was also examined. In the case of the acid dyes, the effect of plasma treatment on color yield was more significant for the milling type dyes with large molecular weight than the leveling type dye with low molecular weight. For the acid metal complex dyes, the hydrophilic groups in the dye molecules did not influence the color yield. Although, in the case of the acid mordant dyes with small molecular weight, the similar effect on color yield to that of the leveling type acid dyes was expected, the effect was almost the same as that of the milling type acid dyes with high molecular weight. The SOX groups should be generated on the surface of wool by plasma treatment, but any effects on color yield for the basic dyes could hardly be observed. Furthermore, the hot water and rubbing fastness were improved by Ar-plasma treatment.