Nylon 6 staple ultramicrofiber(UMF, 0.07d) and regular staple fiber (Regular, 2.0d) were annealed at 100, 130, 160 and 180℃ under tension free for 10 min and 60 min. The treated fibers were dyed with Acid Red 18 and Blue 83. They were adjusted at pH 5.0 of dye bath in buffer solution of CH3COOH/CH3COONa(0.1mol/l). Liquor ratio was kept at 1000:1. Dyeing rate of UMF annealed at 100℃ was decreased, but was increased for regular nylon. Also dye equilibrium of UMF at 100℃ was increased for Acid Red 18, but was decreased for Acid Blue 83. The intensities of X-ray diffraction peaks of UMF increased with increasing annealing temperature. Also the crystallinity of heat-setted fibers by DSC thermogram was well agreed with the tendency of density. Amino end group, moisture regain and water absorbency were decreased with increasing annealing temperature.