Abstract: ob＜x＞jective To investigate the effect of bacterial lipopolysaccharide (LPS) on the ex＜x＞pression of macrophage high mobility group protein B1(HMGB1) and costimulatory molecules. Methods THP-1 and RAW264.7 cells were cultured and stimulated with LPS of different concentrations for 24h. The changes of cell proliferation were detected by CCK8 method . Flow cytometry were used to test the level of apoptosis.The Level of HMGB1 in the culture supernatant and cell was detected by western blot. Q-PCR tested the level of HMGB1 transc＜x＞ription. The ex＜x＞pression of CD80, CD83, and CD86 were detected by flow cytometry. Results CCK8 assay showed that LPS promoted the proliferation of RAW264.7. By contrast, low concentration LPS restrained THP-1 proliferation, while high concentration LPS promoted THP-1 proliferation (P<0.05). Flow cytometry detected that LPS promoted cell apoptosis (P<0.05). Western blot showed the ex＜x＞pression of HMGB1 in THP-1 and RAW264.7 cells culture supernatant raised (P<0.05), while the intracellular HMGB1 decreased (P<0.05). The transc＜x＞riptional level of HMGB1 in THP-1 and RAW264.7 cells went up tested by Q-PCR (P<0.05). The ex＜x＞pression of CD80, CD83, and CD86 increased on these two cells(P<0.05). Conclusion LPS affects THP-1 and RAW264.7 cells proliferation and apoptosis, promotes HGMB1 release, increases the cell surface ex＜x＞pression of CD80, C883, and CD86.