Castration-resistant prostate cancer (CRPC) is an incurable disease with limited treatment options. Herbal supplements are unconventional treatments for a variety of diseases. Active hemicellulose compound (AHCC) is a Japanese supplement discovered by hybridizing several mushrooms used in traditional healing for the purpose of maintaining ‘super immunity’. We report on a 66-year-old gentleman with CRPC with an excellent serologic response to AHCC. This case hypothesizes that AHCC may have potential activity against CRPC.