Provided is a method for preventing postoperative adhesion of an organ in a wound site using the application of an antiadhesive material thereto. The antiadhesive material contains a poly-γ-glutamic acid having a weight-average molecular weight of 600,000 to 13,000,000, or a kinematic viscosity at 37° C. of 2 cSt to 15 cSt when dissolved in distilled water at a concentration of 0.05% by mass and/or a salt thereof, as an effective ingredient. The antiadhesive material may be in a form such as powder, and therefore, for example, is easy to handle even in relatively localized surgery such as endoscopic surgery and can more reliably prevent adhesion.
