The invention belongs to the technical field of molecular biology and relates to application of an exosome derived from human mesenchymal stem cells to preparation of medicines for antagonizing scars or tissue and organ fibrosis. According to the application, the high-purity and high-bioactivity exosome is obtained by subjecting healthy human umbilical cords to primary in-vitro culture, collecting liquid supernatant after amplification, performing low-temperature ultracentrifugation, purifying and the like; the exosome is used individually or added into medicines, health care products and cosmetics according to a proportion to be developed into a product with a bioactivity function, thereby being capable of regulating organism cell signal transduction effectively, inhibiting fibrocyte differentiation and then antagonizing the tissue and organ fibrosis and scar forming. Through experimental verification, the exosome can play a remarkable role in repairing promotion in hypertrophic scar after skin injury, particularly pathological fibrosis proliferation such as scar contracture of the joint parts, hepatic fibrosis and cardiac fibrosis, and is high in safety, little in toxicity and convenient to storage and transport, thereby being wide in application prospect.