Warp and weft knitted fabrics comprising polyethylene terephthalate/Co-PET sea-island bicomponent fibers were fabricated in this study. The knitted fabrics were treated in alkali solution to develop knitted fabrics composed of nano-scale filaments. The structural change and water transport behavior of the alkali-treated knitted fabrics were then compared. Results revealed that the filament diameters decreased from $20{mu}m$ to 850 nm after alkali treatment. The porosities of warp and weft knitted fabrics decreased by 4.8 % and 10.1 %, respectively, whereas their area densities increased by 68.8 % and 67.2 %, respectively. The wicking height and wicking rate of both types of fabric composed of microfilaments increased with prolonged alkali-treatment time. However, the water absorption properties such as absorption capacity and absorption rate of the knitted fabrics composed of nano-scale filaments significantly increased because of their low porosity and high area density.