This experiment was designed to investigate the effects of So-Oochim-tang-Gagam-bang (SOCT-G) on oxidative stress and serotonin metabolism in P815 Mast Cells The effects of SOCT-G on activity of 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging and Super Oxide Dismutase (SOD) in P815 mast cells were investigated. The effect of SOCT-G on content of serotonin in P815 mast cells was investigated. The effects of SOCT-G on expression of 5-hydroxytryptamine transporter (5-HTT), Tryptophan hydroxylase 1 (TPH-1) mRNA in P815 mast cells were investigated. The SOCT-G increased DPPH radical-scavenging activity in P815 mast cells. The SOCT-G increased SOD activity in P815 mast cells. The SOCT-G decreased the intracellular content of serotonin in P815 mast cells. The SOCT-G decreased 5-HTT and TPH-1 mRNA expression in P815 mast cells. This experiment shows that So-Ochm-Tang-Gagam-bang has a significant effect of oxidative stress that help prevent free radical damage. And So-Ochim-Tang-Gagam-bang decreased the intracellular content of serotonin and mRNA expression of 5-HTT and TPH-1. Therefore, further researches are suggested to reveal the anti-depressive effectiveness of So-Ochim-Tang-Gagam-bang.