A pharmaceutical preparation for preventing and/or treating hypertrophic scars, keloid or chronic arthritic diseases comprising as an effective component an erythropoietin antagonist. More specifically, there is provided a pharmaceutical preparation for preventing and/or treating hypertrophic scars, keloid or chronic arthritic diseases comprising as an effective component an erythropoietin antagonist such as an anti-erythropoietin antibody, an erythropoietin receptor protein, etc. This pharmaceutical preparation has excellent prophylactic and/or therapeutic effects on collagenous hyperproliferation such as hypertrophic scars, keloid, etc., or chronic arthritic diseases such as rheumatoid arthritis, etc.