Abstract: OBJECTIVE To investigate the dynamic changes and significance of IL-12p40 and IL-12p70 in bacterial bloodstream infection caused by different pathogens in mice model. METHODS Four models of bloodstream infection of S.aureus, E.faecalis, E.coli and K.pneumoniae in ICR mice were established and evaluated. The contents of IL-12p40 and IL-12p70 in experimental group and control groups of PBS solution at 0.5h, 1h, 3h, 6h, 12h, 24h and 48h were detected by Luminex platform. RESULTS The concentration of IL-12p40 was slightly increased in S.aureus group compared with control group, but increased significantly in E.faecalis group, E.coli group and K.pneumoniae group after 1h of infection, and reached the highest value at 3h after the infection, the peak concentration were (216.36±50.63)pg/mL, (118.32±9.98)pg/mL and (129.19±27.11)pg/ml respectively, and remained at high values after 12h of infection, and the differences were significant compared with control group (P<0.05). The content of IL-12p70 in S.aureus group increased significantly and reached the maximum value after 6h of infection, and its peak concentration was(389.31±118.07)pg/mL. The content of IL-12p70 in E.faecalis group increased significantly after 3h of infection, and the difference was significant compared with control group (P<0.05). The contents of IL-12p70 in E.coli group and K.pneumoniae group reached the maximum value after 3h of infection, which were (42.20±3.54)pg/mL and (62.80±8.37)pg/mL, but the increasing ranges were significantly less than those in S. aureus group and E.faecalis group (P<0.05). CONCLUSION IL-12p40 and IL-12p70 are significantly increased in the 4 bloodstream infection models at the early stage of infection. After the infection with S.aureus or E.faecalis, the concentrations of IL-12p70 is significantly higher than that of E.coli or K.pneumoniae infection. The combined detection of IL-12p40 and IL-12p70 is of some value in differentiating gram-negative and gram-positive bacteria infections.