Color strength is reduced by hydrolysis, reduction or oxidation of disperse dyes during the polyester dyeing process. This discoloration is caused by dyeing conditions such as temperature, pH of the dye bath and the chemical reactions of the dispersing agents, etc. Chemical reduction of certain azo disperse dyes results in lower color yield. To prevent reduction of disperse dyes, sodium salts were added as weak oxidants to the dye bath for polyester fiber. Dyeing was carried out with four commercial azo or anthraquinone disperse dyes in the presence of sodium salts(NaCl, NaBr, NaI). The effects of sodium salts on color strength and fastness are discussed. In the case of azo disperse dyes, color yield increases as the concentration of sodium salts increases.