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The aim of this study is to assess the antibacterial activity of sodium citrate against Streptococcus pneumoniae and several oral bacteria.The antibacterial activity was determined by broth microdilution method. The results showed that although Enterocuccus faecium OB7084 and Klebsiella pneumoniae OB7088 had high tolerance to sodium citrate, several oral bacteria including Fusobacterium nucleatum JCM8532T, Streptococcus mutans JCM5705T and Strep. pneumoniae NBRC102642T were susceptible. Furthermore, the bactericidal activity of sodium citrate against Strep. pneumoniae NBRC102642T was not influenced by pH in the range of 5·0–8·0, whereas that of sodium lactate was weakened at neutral or weak alkaline pH. When Strep. pneumoniae NBRC102642T was treated with sodium citrate for 2 h, many burst cells were observed. However, addition of MgCl2 or CaCl2 to an assay medium weakened the antimicrobial activity although ZnCl2 or MnCl2 did not influence.Independent of pH, sodium citrate inhibited the growth of oral bacteria, which suggests that the mechanism is different from that of sodium lactate.The results presented in this study would be available for understanding the antimicrobial property of sodium citrate.