ObjectiveTo investigate the effect of baicalein （BAI） on SH-SY5Y cell injury in lipopolysaccharide （LPS）-activated BV-2 cells conditioned medium and its mechanism. MethodThe BV-2 cells were activated with 1 mg∙L^-1 of LPS to establish the conditioned medium of the LPS group， and a blank group and groups of BAI with low， medium， and high concentrations （4， 8， 16 μmol∙L^-1） were established. SH-SY5Y cells were cultured with the conditioned medium of each group. The cell viability of BV-2 cells in each group after the intervention was determined by cell counting kit-8 （CCK-8）. The content of tumor necrosis factor-α （TNF-α）， interleukin-6 （IL-6）， and interleukin-1β （IL-1β） in the supernatant of BV-2 cells in each group was determined by enzyme-linked immunosorbent assay （ELISA）. The protein expression of α-synuclein （α-syn） and tyrosine hydroxylase （TH） in SH-SY5Y cells was observed by immunohistochemical （IHC） staining， and the nuclear transfer of nuclear factor kappa-B p65 protein （NF-κB p65， p65） in SH-SY5Y cells was observed by immunofluorescence （IF）. The protein expression of Toll-like receptor 4（TLR4）， p65， phosphorylated p65 （p-p65）， and Myeloid differentiation factor 88 （MyD88） in SH-SY5Y cells was observed by Western blot. ResultAs compared with the blank group， the viability of BV-2 cells in the LPS group was significantly decreased （P<0.01）， and the content of TNF-α， IL-6， and IL-1β in the cell supernatant was significantly increased （P<0.01）. As compared with the LPS group， the cell viability was significantly increased in groups of BAI with low， medium， and high concentrations （P<0.01）， and TNF-α in the cell supernatant was significantly decreased （P<0.01）. The content of IL-6 in the cell supernatant was decreased in the BAI group with high concentration （P<0.05）， and the content of IL-1β in the cell supernatant was significantly decreased in the BAI groups with medium and high concentrations （P<0.01）. The results of conditioned medium cultured SH-SY5Y cells showed that as compared with the blank group， the protein expression of p65 in the LPS group entered into the nucleus and accumulated， and the protein expression of TH was significantly decreased （P<0.01）， while that of α-syn， TLR4， MyD88， and p-p65 was increased （P<0.05， P<0.01）. Compared with the LPS group， the protein expression of p65 in SH-SY5Y cells in BAI groups with low， medium， and high concentrations gradually dispersed into the cytoplasm and had the enhanced protein expression of TH （P<0.01） but the lowered protein expression of α-syn （P<0.01）. The protein expression of TLR4， MyD88， and p-p65 was decreased in the BAI group with high concentration （P<0.05， P<0.01）， the protein expression of p-p65 and MyD88 was decreased in the BAI group with medium concentration， and the protein expression of MyD88 was decreased in the BAI group with low concentration （P<0.05）. There was no significant difference in the protein expression of p65 among groups. ConclusionBAI can inhibit the activation of BV-2 cells， thereby inhibiting the inflammatory response caused by LPS and further inhibiting the damage of inflammation to SH-SY5Y cells. The mechanism may be related to the regulation of the TLR4/MyD88/NF-κB signaling pathway and reduction of the inflammatory response， thus playing a neuroprotective role.