Facing an increasingly aged society, prostate cancer screening, mainly by prostate-specific antigen (PSA), is increasing all over the world, even in Japan. Newly diagnosed prostate cancer has been dramatically increasing and the number of affected patients is estimated to be 78000 in 2020 in Japan. Three-quarters of patients with prostate cancer are older than 65 years old, which makes the cancer suitable for chemoprevention. Herein, we introduce a typical clinical procedure in the diagnosis and treatment of this disease, and report the basic, clinical aspects and prospects of chemoprevention. Within the report, the results in four of phase 3 trials, including the Physicians Health Study II (PHS II), Selenium and Vitamin E Chemoprevention Trial (SELECT), Prostate Cancer Prevention Trial (PCPT) and Reduction by Dutasteride of Prostate Cancer Events Trial (REDUCE) are presented and discussed.