The aim of this study is decolorisation of CI Disperse Dark Blue 148 dye by ozone treatment which is one of the most attractive alternatives for solving the problem of color in textile dyeing effluents. A venturi injection system added dyeing chamber for getting ozone from the ozone generator. And additive (acetic acid and dispersing agent) put in the dyeing. After the coloration, the experimental color, chemical oxygen demand (COD), pH, temperature (degrees C) and conductivity (mu S/cm) were measured. The results encourage the use of the system for decolorisation trials as well as dyebath effluent recycling.