To provide a microorganism carrier for water treatment made of a polyurethane foam which is easy to wet in water, swiftly settles in water after being charged into an aerator, rotates by airation, and is also free from foaming.

An antifoamer is stuck to the surface and inside of a polyurethane foam, so as to compose the microorganism carrier for water treatment. As the antifoamer, acetylene glycol is preferable. Further, as the polyurethane foam, the one obtainable by the reaction between polyol and isocyanate, and, in which, as the polyol, polyether polyol or polyether polyester polyol partially containing an ester radical is used is preferable.