The dyeing properties of milling type acid dyes with various chemical constitutions in one bath dyeing of nylon/wool blends were studied and the proper dyeing condition to get solid color by using the reserving agent was also examined. When nylon and wool were dyed in the same bath, the dye-uptake of wool decreased but that of nylon increased in comparison with the case of being dyed separately. As the number of sulphonic acid group in the dye of same chemical class increased, the dye-uptake of nylon and critical depth decreased. When nylon and wool wire dyed in the absence of each other, the reserving agent retarded the initial dyeing rate of nylon, but increased the final dye-uptake, on the other hand the dye-uptake of wool was not affected. When nylon and wool were dyed in the same bath, the addition of reserving agent increased the dye-uptake of wool, the proper concentration of reserving agent for solid color was obtained. The increase of the number of sulphonic acid group made it possible to reduce the amount of the reserving agent solid color.