In this paper，an acoustic diagnosis method for vacuum pump is described. There is an essential requirement that the vacuum pumps equipped in a semiconductor plant，should keep running twenty-four seven without troubles. A periodical maintenance，where the worm seals of the pump are exchanged for new ones，is a popular method to satisfy the requiremen. However，abrasion speed of the pump has huge differences among individuals. More sophisticated diagnosis method should be replaced for the periodical maintenance to optimize the period of the maintenance and reduce the maintenance cost. The acoustic diagnosis method for seals' abrasion has been developed to utilize sound of refrigerant leakage of the pump as an indirect index of seals' abrasion. A prototype of diagnosis tool has been implemented and evaluated both in a laboratory and in a semiconductor factory over six months. Capability for a field diagnosis tool is confirmed through the field tests.