The effect of structural factors on the comfortabilities of knit fabrics has been studied to provide an information on structural design of knit-wears used specially for summer. To improve the comfortabilities, the fabric should absorb the sweat exuded from human body and give it out rapidly, and also have a good moisture permeability. To measure these properties, simple testing devices were newly designed and built. The structural variables considered in the experiment were fiber type, the blend ratio of fibers, and the twist level of yarn. All the variables gave a significant effect, which could be objectively evaluated based on the theoretical model introduced.