Abstract: In order to improve the dyeing capacity of anionic dyes onto cotton fabric in reverse micelles, the nonionic mixed reverse micelles were prepared by adding Span40 in TX-100 reverse micelles. And the system was used as dyeing media for coloration of direct yellow brown 3G onto cotton fabric. The effect of Span40 on the maximum water solubilization, water diameter, packing density, conductivity and dyeing properties of reverse micelles were investigated, respectively. The results indicated that the maximum values of the maximum water solubilization were observed when the ratio of Span40 was 50%. The water diameter and packing density of reverse micelles increased with increasing the ratio of Span40, which caused the lower conductivity. The repelling force and competitive adsorption between dyes and cotton fabric were decreased with increasing ratio of Span40, and the higher adsorption and dyeing properties in reverse micelles were obtained.