Novel and effective anti-fibrosis agents are obtained. An anti-fibrosis agent containing an antagonist for integrin α8β1 is used. In addition, used is an antagonist containing an anti-integrin α8β1 antibody that specifically binds to at least one amino acid in a cap subdomain of an integrin α8 chain and a periphery thereof. Also, used is an anti-fibrosis agent containing an anti-integrin α8β1 antibody that specifically binds to R120 of an integrin α8 chain and a periphery thereof or S132 and a periphery thereof. Note that the above antagonists may each be an anti-integrin α8β1 antibody capable of binding to any of integrins α8β1 derived from a human, mouse, and rat.