Hemorrhagic fever with renal syndrome (HFRS) is a severe acute viral disease with pathological changes of impaired capillary and small vessels and thrombocytopenia. In this study, serum thrombospondin (TSP)-1 concentration in patients with HFRS was determined to explore its possible role in the pathogenesis of HFRS. The concentration of TSP-1 was measured using a competitive enzyme-linked immunoabsorbent assay. Significantly decreased levels of serum TSP-1 were observed in HFRS patients at febrile and hypotensive phases compared with those in the controls. The serum levels of TSP-1 in HFRS patients with more severe clinical types was reduced more profoundly than those in patients with milder clinical types at febrile and hypotensive phases, although the differences in TSP-1 were not significant. It was indicated that insufficient production or increased consumption of TSP-1, or both of these, may contribute to the impairment of capillary and small vessels and the development of hypotension at the early stage of HFRS, and the decreased degree may be associated with disease severity.