The alkaline dissolution behavior and dyeing properties of acid dyes and reactive dyes on sea-island type ultrafine nylon fiber were investigated in this study. The alkaline dissolution behavior was very dependent on the concentration of NaOH and temperature, the most appropriate condition was to treat the fabric with 10 g/l NaOH for 30 min at $90^{circ}C$. The dye uptakes of the ultrafine nylon and regular nylon fiber decreased as the dyebath pH increased. Although the exhaustion percentages of the ultrafine nylon fiber were higher than those of the regular nylon at all pHs, the color strength of the dyed ultrafine fabrics were weaker due to the increased surface area per unit mass. The washing fastness of the ultrafine nylon fibers dyed with the reactive dyes was found to be excellent.