In this study, we examined the effects of Lentinula edodes mycelia (LEM) on fatigue and immune function in healthy subjects. 22 people were randomly assigned in a 1:1 ratio to the LEM ingestion group and the placebo group. Daily oral ingestion of LEM for 4 weeks (600 mg/day) significantly improved the VAS fatigue score compared with before treatment (p<0.01). Additionally, NK cell activity was increased by ingestion of LEM (p<0.01) and was higher level compared to the placebo group (p<0.05). These results indicate that oral ingestion of LEM may improve the feeling of fatigue and immune function.