The present invention is to provide an agent for treating Crohns disease that is of unknown cause and for which no radical therapeutic drug is present. Provided is an agent for preventing or treating Crohns disease, comprising an organic acid polymer represented by the following formula: [(O1/2)3Ge-A-CO2H]n, wherein n is 100-1,000, and A is a lower alkyl group. Preferably, A is a C1-C3 lower alkyl group and the degree of polymerization n is 200-900. The organic acid polymer according to the present invention is effective as an agent for treating Crohns disease.
