The cotton fabrics treated with 50% N-methylmorpholine-N-oxide(50% NMMO) and 75% N-methylmorpholine-N-oxide(75 % NMMO) aqueous solution were examined in terms of the dyeability comparing with those of regular cotton fabrics. The dyeing rate was increased with the increase of the concentration of NMMO in the treatment aqueous solution. The NMMO treatment increased the diffusion coefficients and decreased the activation energy of direct dye onto cotton fabrics. This means that the NMMO could change the micro-structure of cotton fabrics.