Underwear made of plain and 1$\times$1 rib-knit cotton fabric were laundered to evaluate the change of the size and the tensile properties. For laundering pulsator and drum washers were used. After 30 washing cycles the amount of shrinkage and the extension were different with washer types. Underwear laundered by the drum type was shrunken in the neck line armhole line and hem line were extended and the bodice width and side length were shrunken,. Tensile strength of the knitted fabric was not decreased through repeated washings because the fabric density was increased. But it was confirmed by SEM that the surface of the fiber was damaged by washings.