Abstract: Objective understand the characteristics of influenza B viruses circulation and serum antibody level in population in Ningbo from 2009 to 2010.Methods Samples were collected from the patients in sentinel hospitals for influenza virus isolation, and blood samples were taken from healthy people in July 2009 and March 2010 to detect influenza B viruses antibodies with magglutination-inhibition reaction. Results The circulation of influenza B virus Victoria lineage was active from 2009 to 2010,two circulation peaks were observed and new variant strains were detected since June. The serum antibody positive rate was 42.12% for the samples taken from the healthy people in July 2009 and 51.11% for the samples taken in March 2010.Conclusion The circulation of influenza B virus Victoria lineage was related with the variation of its hemagglutinin gene and the antibody level to influenza B virus Victoria lineage increased obviously in population in Ningbo from 2009 to 2010.