Alkali hydrolysis of sea-island PET 0.02denier microfiber were compared to those on the fabrics of the 0.06denier microfiber. In the dissolution of the sea component out of sea island type ultra-microfiber, it is important to determine the optimum division and divided material. Weight reduction of sea island ultra-micro sea island fiber was faster than regular PET about 10 times. Also 0.2denier sea-island ultra-micro sea island fiber has better color fastness (washing, friction, and daylight) than 0.06denier level sea-island ultra-microfiber. In this study, 0.2denier ultra-micro sea island fiber shows the possibility of high value product.