For centuries, Corydalis Rhizoma has been used in Korean traditional medicine. Tetrahydropalmatine is an alkaloid compound and a prominent anti-inflammatory agent found in plants, including Corydalis yanhusuo. However, the therapeutic mechanisms of tetrahydropalmatine are still not well understood. To provide insight into the biological effects of tetrahydropalmatine, we examined its influence on lipopolysaccharide (LPS)-induced interleukin (IL)-8 production in the human monocytic cell line THP-1. In the present study, IL-8 production was measured using enzyme-linked immunosorbent assay, reverse transcription-polymerase chain reaction, and mitogen-activated protein kinase (MAPK) activation, as determined by western blot analysis. Tetrahydropalmatine inhibited LPS-induced IL-8 production in a dose-dependent manner. Furthermore, tetrahydropalmatine inhibited extracellular signal-regulated kinase and p38 MAPK phosphorylation, which suggests that tetrahydropalmatine inhibits IL-8 secretion by blocking MAPK phosphorylation. Taken together, these findings may help elucidate the mechanism by which tetrahydropalmatine modulates THP-1 cell activation under inflammatory conditions.