RASSF1A gene cloned from 3p21.3 region is a novel candidate tumor suppressor gene. The aberrant methylation of CpG lands in the promoter region is the major inactivation mechanism of RASSF1A, and is significantly involved in the genesis and development of multiple solid tumors including prostate cancer. The methylation status examination of RASSF1A could serve as an important technique for the early diagnosis of prostate cancer, while methylation inhibitor is likely to become a novel therapeutic agent.