The viral IL-10 (vIL-10) gene of Epstein-Barr virus (EBV) exhibits high homology with human IL-10 gene. In order to characterize vIL-10 gene in EBV-infected children in China, DNA sequencing of this gene was performed in 249 cases of EBV-associated infectious mononucleosis, 46 EBV-associated hemophagocytic lymphohistiocytosis and six chronic active EBV infection. Eight silent and seven nonsilent mutations were identified, of which silent mutation c9980a was prominently presented (75.7%, 228/301) in the studied cases. Two subtypes of the vIL-10 gene, including pattern B95-8 and pattern SPM (mutation in the signal peptide), were identified. Pattern B95-8 was the dominant subtype in infectious mononucleosis, EBV-hemophagocytic lymphohistiocytosis and chronic active EBV infection. These results indicated that the vIL-10 gene exists as a highly conservative form in -EBV-associated infection in Chinese children.