A water-soluble spiroaxazine may be successfully applied directly as dye to produce photochromic silk fabric. Molecular modelling, using the CAChe system, provides a good prediction of its photochromic properties. The dyed fabric shows good colour build-up under UV irradiation and reverts slowly to the original colour when the T-W source is removed. It is observed that wet fabric shows better photochromic performance than after drying.