This study was to investigate the effect of sinomenine by LPS-induced MAPK phosphorylation in endothelial cells. Endothelial cells were challenged with different doses LPS and/or treated with sinomenine at three concentrations (1, 5, or 10 μg/mL) in pathological model, drug safety, treatment and prevention experiments. The cells were incubated at 37 °C in a cell incubator total for 24 h. The lysate cells were collected and analyzed the phosphorylation of ERK1/2, JNK and p38 by MAPK phosphoprotein assay whole cell lysate kit. As expected, LPS could significantly elevated phosphorylation of ERK1/2, JNK and p38, but sinomenine not. The results revealed that sinomenine significantly reduced the phosphorylation of ERK1/2 and p38 in treatment experiment, and inhibited phosphorylation of ERK1/2, JNK and p38 in prevention experiment. Our findings demonstrated that sinomenine protects endothelial cells from LPS-induced inflammation, which might be associated with depressing MAPK signaling pathway.