This study were made on the air permeability of weft knitted fabrics using cotton yarn as raw materials. It is general assumption that the air permeability as weft knitted fabrics are resulted from the sum of two parts. The one is a nozzle part such as space among yarns in cotton knitted fabrics, and the other is a capillary part such as space among fibers in knitted yarn. Based on this assumption we had studied on the three basic weft knitted structures as plaint 1$ imes$1 rib and interlock stitches in connection with air permeabilty. And we had made the regression equations between parameter A(nozzle part), B(capillary part) and air-permeability of cotton knitted fabrics by means of stepwise regression analysis. From the analysis, the f311owing results were obtained: Vupia, n) : 7.36639+203.03799A+371.05482B, Vunb)=26.27621+ 256.03855A+281.64791B, Vu, n‥‥1~k)= 56.51290+56.78075A+54.97715B, Vu, o, at)=28.807)6+214.90318A+71.51714B.