Abstract: Indigo acid-leuco was used to dye vinylon in order to improve the color yield of vinylon. The dyeing method and dyeing parameters such as pH value of dye bath, dyeing temperature, concentration of dyestuff, sodium hydrosulfite and salt were investigated. The results showed that vinylon was successfully dyed with indigo acid-leuco. Dye uptake of vinylon was higher with increasing the concentration of dyestuff. Vinylon dyed at 90-100 ℃ for 30 minutes at pH value 4-5 and sodium hydrosulfite 8g/L featured higher color yield. Vinylon exhibited signifi cant softening and contraction when dyeing temperature was above 110 ℃. Meanwhile salt had accelerating effect for dyeing vinylon with indigo acid-leuco.