High-mobility group box protein 1 (HMGB1) is nuclear protein conserved among almost all eukaryotic cells. HMGB1 is thought to be a danger signal mediator when it is released both actively from activated immune cells and passively from dead cells into extracellular milieu upon pathogen infections or sterile inflammations. Released HMGB1 act as an inflammatory cytokine and promote inflammatory disorders. However, in vivo function of HMGB1 is still elusive. Recently we have established Hmgb1 gene conditional knockout (KO) mice and examined the role of HMGB1 in innate immune responses, inflammation and cancer. Interestingly, we observed that the number of glanurocytic neutrophils are decreased when mice were innoculated HMGB1 KO tumor cells. We would like to show and discuss these data.