New anthraquinone disperse dyestuff of sparing aqueous solubility, of the formula I A - Y - O - COSR (I) wherein A is the radical of an anthraquinone dyestuff, Y is an alkylene or aralkylene bridge which is bonded to the anthraquinone nucleus directly or through a bridge member and which is optionally substituted by a hydroxyl group and/or is interrupted by an oxygen atom, and R is an optionally substituted aliphatic, cycloaliphatic, or aromatic radical. The new dyestuffs dye polyester fibers in fast blue shades.