Platycodon grandiflorum have been used as a traditional remedy and food source. This study was performed to investigate the immunomodulating effects of Platycodon grandiflorum in mouse, using ex vivo experiments. Six to seven-week old mice were fed ad libitum on a chow diet, and water extract of Platycodon grandiflorum was orally administrated at two different concentractions (50 and 500 mg/kg B.W./day) every other day for four weeks. In ex vivo experiments, the highest proliferation of splenocytes and levels of cytokine (IL-$1{eta}$, IL-6, TNF-${alpha}$) production were observed in 500 mg/kg BW/day supplementation group for all three cytokines stimulated by LPS. In conclusion, this study suggests that Platycodon grandiflorum extracts may enhance the immune function by regulating the splenocytes proliferation and cytokine production capacity by activating macrophages in mice.