Lentinula edodes mycelia extract has been reported to maintain and improve immune function and QOL in cancer patients. In this study, the effects of Lentinula edodes mycelia extract on immune function were investigated in 10 healthy volunteers. Ten subjects were administrated Lentinula edodes mycelia extract orally for 20 weeks on average (846 mg / day ), and the immunological function (IFNγ production amount, IL-10 production amount, lymphocyte subset)was evaluated before and after ingestion at Fukuoka Tenjin Southern Clinic. Immune function following ingestion of Lentinula edodes mycelia extract showed a tendency of IFNγ production to increase, IL - 10 to decrease, and IFNγ / IL - 10 production ratio to be improved remarkably. No significant change was observed in lymphocyte subsets such as regulatory T cells before and after ingestion. Adverse events during the intake period were not observed. It was suggested that oral intake of Lentinula edodes mycelia extract has an action to improve the immune function of healthy adults.