The most well-known medicinal plant, Panax ginseng (P. ginseng), contains various phytosterols and bioactive triterpene saponins (ginsenosides). Squalene synthase is a key regulatory enzyme for triterpene biosynthesis and overexpression of the squalene synthase confers the hyper-production of triterpene saponins to form transgenic ginseng. In this study, we have investigated whether and how transgenic P. ginseng modulates an inflammatory reaction in a stimulated human mast cell line, HMC-1. It was found that transgenic P. ginseng inhibited the production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-8, and the expression of cyclooxygenase-2 in phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore A23187 (PMACI)-stimulated HMC-1. Additionally, we have shown that transgenic P. ginseng suppressed the intracellular calcium level induced by PMACI. These results provide new insights into the pharmacological actions of transgenic P. ginseng as a potential molecule for use in therapy in mast cell-mediated inflammatory diseases.