In the one-bath dyeing of polyester/wool blended fabrics by disperse/acid dyeing system, the effect of carrier on dyeing property and the mechanism of carrier action on wool dyeing were studied. As the effect of carrier on wool dyeing by acid dyes, initial dye uptake increased by carriers as the increase of hydrophobic character of acid dye. As the mechanism of carrier action, the effect of loosening fiber structure, antiaggregation of dye and building carrier film acted compositely and among them carrier film effect affected most. As the effect of carrier on wool staining by disperse dyes, initial staining increased but final staining decreased by carriers.