The weight reduction properties and dyeing properties of sea-island type PET supermicrofiber were compared with those of normal sea-island type PET microfibers. The alkaline dissolution behavior of microfibers were monitored using a cationic dye staining method. The dye uptake of finer microfibers commences at lower temperatures and showed faster rate of dye uptake. The build-up and wet fastness properties of disperse dyes on finer microfbers were relatively poor since more dye was required to achieve a given depth of shade due to the large surface area. Also, the low temperature dyeing of microfibers produced higher color yield than normal high temperature dyeing because of less dye migration to the coarser fibers during dyeing.