Temporarily solubilized azo disperse dyes containing ${eta}$-sulfatoethylsulfonyl group were applied to PTT fabric and feasibility of dispersant-free dyeing was investigated. The color yields of the dyes on PTT fabric were found to be dependent on dye bath pH while not much on dyeing temperature. The optimum results were obtained at pH 5-6 and $110^{circ}C-120^{circ}C$. The dyes showed good build-up properties on PTT fabric. Washfastness were fair to moderate and lightfastness were somewhat poor. The COD levels of the dyeing effluent from the temporarily solubilized disperse dye were much smaller than those from commercial disperse dyes.