The interaction between a milling type acid dye-C.I. Acid Blue 113 and non-ionic surfactants were measured by the spectrometric continous variation method and change of cloud point, with variations in carbon number of alkyl chain and in length of ethylene oxide chain of that surfactants. Effects of these surfactants on the dyeing rate of the dye on wool were also investigated and discussed in view of complex formation with the dye. The results of this study are summarized as follows: 1) By a series of the surfactants having the same hydrophbic part, the mole ratio of surfactant to dye and association constant of complex decrease with increase in length of ethylene oxide chain. 2) The mole ratio of surfactant to dye and association constant however, show more higher values as the carbon numbers of hydrophobic part increases when a series of the surfactants having the same length of ethylene oxide chain in concerned. 3) The cloud point of the surfactants is raised by the presence of the dye. 4) The rate of the dyeing on wool is slow downed as the association constant increases, but does not greatly affected by the mole ratio of surfactant to dye. 5) The levelling action of non-ionic surfactants greatly depends on their interactions with dye in dye solution.