An adhesion-preventing material having a high adhesion-preventing effect has been demanded. An adhesion-preventing material including a sterilized biocompatible sponge-like laminate, wherein the sponge-like laminate comprises a sponge-like first layer and a sponge-like second layer each of which is at least partially crosslinked with a curing agent and comprises a low-endotoxin alginic acid monovalent metal salt, the alginic acid monovalent metal salt in the first layer has a weight average molecular weight of 10,000 to 2,000,000, the alginic acid monovalent metal salt in the second layer has a weight average molecular weight of 1,000 to 1,000,000, the weight average molecular weights are measured by a GPC-MALS method after a decrosslinking treatment, and the weight average molecular weight of the alginic acid monovalent metal salt in the first layer is higher than that in the second layer.