The high- and the low-molecular weight hyaluronic acids (HMW-HA and LMW-HA, respectively) showed different biological activities in inflammation. However, the role of LMW-HA in inflammatory response is controversial. In this study, we aimed to investigate the effect of bioactive hyaluronan (B-HA) on lipopolysaccharide (LPS)-induced inflammatory responses in human macrophages and mice. B-HA was produced from HA treated with glycosylated recombinant human hyaluronidase PH20. Human THP-1 cells were induced to differentiate into macrophages. THP-1-derived macrophages were treated with B-HA, LPS, or B-HA+LPS. The mRNA expression and the production of inflammatory cytokines were determined using quantitative real-time PCR and enzyme-linked immunosorbent assay. The phosphorylation levels of proteins in the nuclear factor- B (NF- B), mitogen-activated protein kinase (MAPK), and IRF-3 signaling pathways were measured using Western blot. The efficacy of B-HA was assessed in a mouse model of LPS-induced inflammation. Results showed that B-HA inhibited the expression of TNF-α, IL-6, IL-1, and IFN-β, and enhanced the expression of the anti-inflammatory cytokine IL-10 in LPS-induced inflammatory responses in THP-1-derived macrophages and . B-HA significantly suppressed the phosphorylation of the TLR4 signaling pathway proteins p65, IKKα/β, I Bα, JNK1/2, ERK1/2, p38, and IRF-3. In conclusion, our results demonstrated that the B-HA attenuated the LPS-stimulated inflammatory response by inhibiting the activation of the TLR4 signaling pathway. B-HA could be a potential anti-inflammatory drug in the treatment of inflammatory disease.