The purpose of this study was to investigate the comparative effect of elastane yarn on some mechanical and comfort properties of single jersey, 1x1rib and interlock knitted fabrics in relation to elastane yarn presence in the combed ring cotton yarn. An elastane yarn accounts for about 5% content (40denier = 133Ne) while cotton accounts for 95% content (35 Ne) in the 28Ne combed cotton/elastane blended yarn (cotton/elastane = 95/5%) and the elastane is not skin friendly (naked filament) with the cotton yarn. The comparison was done between cotton/elastane yarn knitted fabrics and 100% cotton yarn knitted fabrics and within the three structures such as single jersey, 1x1 rib and interlock. The test was done for the bursting strength, abrasion, pilling resistances and air permeability of single jersey, 1x1rib and interlock knitted fabrics using digital bursting strength tester and Martindale abrasion and pilling tester and air permeability tester by conditioning for 24hours at 21oc±1 and 65±2% RH. As found from the study, the presence of elastane yarn influences significantly by decreasing the bursting strength and increasing abrasion resistance of the three knitted fabrics. The pilling resistance of knitted fabrics such as 1x1rib and interlock decreased while single jersey knitted fabrics increased significantly due to 5%elastane yarn in 95% combed cotton yarn. Together with the air permeability; the loop length, wales per centimeter, thickness, shrinkage percent and tightness factor are also investigated since they are deciding factors of air transmission of knitted fabrics. It was found out that the air permeability property of single jersey, 1x1rib and interlock knitted fabrics made from 100%cotton and cotton/elastane yarns is significantly different from each other and all of the knitted fabrics have lower air permeability with cotton/elastane blend yarns as compared to 100%cotton yarn.