The present invention relates to a method for purifying a mixture of cysteine-linked antibody-drug conjugates, wherein the amount of non-conjugated antibody is in the range of 0-40% by weight, using hydrophobic interaction chromatography (HIC). The mixture is loaded onto a preparative HIC column using a 0.2-1.5 M aqueous salt solution, in which non-conjugated antibody is collected in a flow-through fraction, followed by elution of a purified mixture of cysteine-linked antibody-drug conjugates using a 0-100 mM aqueous salt solution.