Gynostemma pentaphyllum is a popular herbal tea in China and some Asian countries. The modulatory function of G. pentaphyllum total plant extracts on immune cells was evaluated in this study. The extract was intraperitoneally injected into mice for 5 consecutive days. The production of antibodies from B cells or cytokines from T cells was determined mainly with ELISA. After the treatment, serum IgM and IgG2a were significantly enhanced and showed dose-dependent effect. Moreover, serum IgA and IgG1 were also increased when received the extract at the doses of 0.05 or 0.50 g/kg/day. In addition to the serum levels, the injection of the extract enhanced the production of all antibodies from LPS-activated spleen cells. Furthermore, more cytokines were secreted from Con A-stimulated splenocytes of G. pentaphyllum-treated mice. Our results suggest that the extract of G. pentaphyllum might promote immune responses through the activation of T and B cells.