The subject of this work was the discolouration of one side of dyed cotton fabric using UV-C radiation, testing for fastness to that external radiation agent. This was studied through selection of different dyes used for dyeing cotton fabrics, namely three direct dyes, two vat dyes, seven reactive dyes, one sulphur dye, one azo dye and three mixtures of reactive dyes. The results for colour differences between the original dyed fabric and the fabric discoloured through UV-C radiation treatment show that, in general, the highest values were obtained for the reactive dyes and their mixtures, with the lowest values, in general, for the sulphur, vat and azo dyes, and intermediate values for direct dyes