The growth of the temporal defaunation on the bottom sediment often occures in eutrophic inner bays during oxygen depletion period in summer. Paraprionospio sp., A-type, is selected as a typical spiece, which is well-known as an organic pollution indicator and a dominant polychaeta in most eutrophic bays. The physiological tolerance to low oxygen concentration is examined to get the dose-responce relationship. At 20°C, respiration rate decreases when D.O. concentration becomes below 3mg/l. But high survivorship is observed for the low oxygen condition. The tolerance limit is estimated as D.O. concentration below 2mg/l maintained for more than 2 days. Reduced sub stances on the bottom serface under anaerobic condition might be more effective rather than oxygen depletion itself in the bottom water.