Abstract: The cotton fabrics were dyed with hydrolyzed and un-hydrolyzed active bright red X-3B. The dyeing property of modified and unmodified cotton fabric were investigated by testing the absorption spectroscopy of hydrolyzed and un-hydrolyzed active dye solution and the color indexes (L﹡, a﹡, b﹡, c﹡values and K/S value) of the dyed fabrics. It was found that the differences of the UV-Vis absorption spectroscopy of dye solution between hydrolyzation and un-hydrolyzation were very large and the colour of dye solution was light when the active dye was hydrolyzed. The uptake and fixation of the dye, and the colour and K/S valu of the dyed fabric could be influenced by the the hydrolyzation of dye. The dyeing property of cotton fabric could be improved when the fabrics were modified with reactive and non-reactive cationic modifiers. The uptake and fixation of the active dye and hydrolyzed active dye on the cotton fabric which was treated with ractive modifier were improved, especially the fixation.