Decomposition of disperse dyes in alkaline dyebath was measured using thin-layer chromatography. The stability of reactive dyes in aqueous solution with and without disperse dyes was studied by measuring hydrolysis rate of the dye at various temperature and pH condition. Disperse dyes were decomposed in reactive dyeing condition and the tendency of decomposition varied significantly according to the structure of the dyes. The presence of disperse dye decreased the amounts of hydrolyzed reactive dye in one bath dyeing system.