Modal realism is an ontological claim according to which there exist many possible worlds just like our actual world. Since it is so hard to believe, modal realism has only a few advocates. However, it is well known that alternative theories have serious problems. It is one of the central issues of metaphysics to find a persuasive way to reject modal realism. In this paper, I will suggest that it could be accomplished with help of metaontology-one of the topics of metaphysics which has recently discussed intensely. I will show how we could argue against modal realism from the metaontological point of view.