Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a newly discovered bunyavirus, SFTS virus (SFTSV), and causes high fatality (12% on average and as high as 30%). The objective of this study was to determine whether SFTSV could be transmitted from person to person. We analyzed sera of 13 patients from two clusters of unknown infectious diseases that occurred between September and November of 2006 in Anhui Province of China for SFTSV antibody by indirect immunofluorescence assay and for SFTSV RNA by RT-PCR. We found that all patients (n=14) had typical clinical symptoms of SFTS including fever, thrombocytopenia, and leukopenia and all secondary patients in both clusters got sick at 6-13 days after contacting or exposing to blood of index patients. We demonstrated that all patients in cluster 1 including the index patient and nine secondary patients and all three secondary patients in cluster 2 had seroconversion or fourfold increases in antibody titer to SFTSV and/or by RT-PCR amplification of SFTSV RNA from the acute serum. The index patient in cluster 2 was not analyzed because of lack of serum. No person who contacted the index patient during the same period, but were not exposed to the index patient blood, had got illness. We concluded that SFTSV can be transmitted from person to person through contacting patient's blood.