Abstract: Objective To investigate the effect of bacterial lipopolysaccharide (LPS) on the expression of macrophage high mobility group protein B1 (HMGB1) and costimulatory molecules. Methods THP-1 and RAW264.7 cells were cultured and stimulated with 100, 200 and 1 000 μg/L LPS for 24 h. The cell proliferation was detected by CCK8 assay. The cell apoptosis was detect by flow cytometry. The level of HMGB1 in the culture supernatant and within the cells was detected by Western blot. The transcription of HMGB1 was examined by Q-PCR. The expression of CD80, CD83, and CD86 were detected by flow cytometry. Results LPS promoted the proliferation of RAW264.7 cells. LPS inhibited the proliferation of THP-1 cells at a low concentration, but promoted THP-1 cell proliferation at a high concentration (P<0.05). LPS promoted the apoptosis of both THP-1 and RAW264.7 cells (P<0.05). The expression of HMGB1 increased in THP-1 and RAW264.7 cell culture supernatant (P<0.05), but intracellular HMGB1 decreased (P<0.05). The transcriptional level of HMGB1 went up in THP-1 and RAW264.7 cells (P<0.05). The expression of CD80, CD83, and CD86 increased on these two cells (P<0.05). Conclusions LPS affects the proliferation and apoptosis of THP-1 and RAW264.7 cells, promotes HGMB1 release, and increases the expression of CD80, C83, and CD86 on cell surface.