Provided is a novel method for inhibiting the proliferation of a plant pathogenic bacterium using a bacterium belonging to the genus Trichoderma. A method for inhibiting the proliferation of a plant pathogenic bacterium, said method being characterized by comprising culturing a strain HNT-01 microorganism that is capable of inhibiting the proliferation of plant pathogenic bacteria and belongs to the genus Trichoderma and then seeding the cultured microorganism in plant soil.