Myogenesis is required to generate skeletal muscle tissue and to maintain skeletal muscle mass. Decreased myogenesis under various pathogenic conditions results in muscular atrophy. Through a small screening of Japanese traditional (Kampo) medicines, hachimijiogan (HJG) was shown to promote the myogenic differentiation of C2C12 myoblasts through the upregulation of myogenin. In tumor-bearing cancer-cachectic mice, HJG was also found to have a protective effect against cancer-cachectic muscle wasting. This effect was significant when HJG was administered in combination with aerobic exercise by treadmill running. Moreover, HJG ameliorated the cellular atrophy of C2C12 myotubes induced by treatment with conditioned medium derived from a colon-26 cancer cell culture. In addition, HJG suppressed H2O2-dependent myotube atrophy, suggesting that HJG could reverse the atrophic phenotypes by eliminating reactive oxygen species.