The purpose of this study was to determine the effect of yarn count (card yarn Ne 30, 40, 50 and 60), stitch (plain, 1$ imes$1 rib and interlock), temperature(2$0^{circ}C$, 3$0^{circ}C$ and 4$0^{circ}C$) and relative humidity (55%, 65% and 80%RH) of cotton knitted fabrics on the water vapor permeability. The results were as follows : The weight of permeated water vapor can be functionalized with the distance between the sample knitted fabrics and absorbent as $y=ae^{-x}+b$. The effective distance between the sample knitted fabrics and the absorbent was found to be about 11.35 mm at plain and rib stitch, and interlock stitch was about 12.00 mm. The water vapor permeability of rib stitch was excellent rather than that of plain and interlock stitch at constant temperature and humidity, but regardless of yarn count and stitch structure, that was nearly leveled at 1 hour, however that of plain and rib stitch had superior to interlock stitch of fine yarn count at 3 hours.