In this article, effect of the dyeing and mechanical properties were investigated on the polyester ultramicro fiber(UMF) and knitted fabric varying fiber fineness(0.01d and 0.05d). By a treatment with NaOH solution, sea-ingredient was removed and polyester micro-fiber was revealed. The dyeing, build-up and fastness properties of the fiber and fabrics were observed. We used C.I. Disperse Red 60 and Blue 56 for dyeing property and eight Lumacron dyes for build-up property and colorfastness. At low temperature dyeing(100℃), the dyeing rate of 0.01d-polyester UMF increased more than that of 0.05d-polyester UMF with Disperse Red 60 and Blue 56 whereas dyeing rate of 0.05d-polyester UMF were increased more than that of 0.01d-polyester UMF at high temperature(120℃), The colorfastnesses of the 0.05d-fiber knitted fabric such as washing, rubbing and light was higher than those of the 0.01d-fiber knitted fabric.