Abstract: This invention may be described as follows. (1) A defoaming agent for the production of highly elastic soft and semi-rigid polyurethane foam, having as a main component thereof an organio silicone compound represented by the following formula (I) ##STR1## wherein each R.sup.1 is a monovalent hydrocarbon group of one to eighteen (18) carbon atoms, R.sup.2 is a monovalent hydrocarbon group of one to eighteen (18) carbon atoms or an organic substituent, and x and y are each not less than 1, providing x+y equals a number between 3 to 8. A method for the production of a highly elastic soft and semirigid polyurethane foam with said defoaming agent per formula (1) and a highly elastic soft polyurethane foam and a semirigid polyurethane foam produced by this method are also taught.