Because acid dyes and reactive dyes require acidic condition for adsorption and alkaline condition for fixation respectively, it is difficult to dye nylon/cotton blends in one-bath one-step dyeing method. In this paper we tried to find out the suitable dye and dyeing condition for one-bath one-step dyeing of nylon/cotton blends. MNT type reactive dyes showed higher exhaustion on cotton as compared with MCT type dyes at neutral pH, which means that the MNT type reactive dyes are preferable for one-bath one-step dyeing method. The optimum condition for one-bath one-step dyeing of nylon/cotton blends was found to be pH 7. Wash fastness of fabrics dyed with half-milling type acid dyes was superior to that of fabrics dyed with levelling type acid dyes, when MNT type reactive dyes were used together.