In one bath dyeing of polyester/cotton blended fabrics using disperse/vat dyes, the effects of one bath dyeing condition on the levelling properties of vat dyes were studied and the proper condition for good levelling of vat dyes was examined. Though disperse dyeing condition and the existence of disperse dye had some bad effects on levelling, the levelling properties of vat dyes in one bath dyeing were better than those of normal vat dyeing. The levelling properties were enhanced by levelling agent and raising temperature. Good levelling was attained at 10 : 1 liquor ratio.