This study was conducted to investigate the effects of a powder of steamed and freeze-dried mature silkworms (SMSP), Bombyx mori, on hair growth/loss in vivo in C3H mice. Topically applied SMSP for at least 10 days or longer showed potent hair growth promoting activity. SMSP-treated mice showed increase in hair weight significantly compared with control mice which were not treated with SMSP. Orally administered SMSP also showed hair growth promoting activity, which was lower than that when applied topically. In conclusion, SMSP was identified as a potential candidate for a novel hair-loss preventing and/or hair-growth promoting agent, which shortened the telogen phase to advance the following anagen phase in C3H mice in vivo when SMSP was applied topically for at least 10 days or longer.