In order to measure the change of constructional and some properties of knitted under wears by laundry, constructional properties, such as fabric count , yarn count, loop length and cover, factor, and some properties , such as shrinkage, tearing, strength, air permeability, electrostatic charge of under wears sold in the market were tested. The results of the experiment can be summarized as follows.1. Interlock and rib were increased in wale direction after laundry and decreased in course direction , plain was decreased, in both direction after laundry. 2. Loop form of plain was changed more than those interlock and rib after laundry. 3. Tearing strength was decreased 51% in wale direction, and 70% in course direction after 20 times laundry. Air permeability was generally increased. 4. Electro static charge was increased 9 times after laundry.