Asymmetric dimethylarginine(ADMA) is an endogenous inhibitor of NO synthase(NOS) and can decrease the production of NO via inhibition of NOS competitively.ADMA is reported to be implicated in the pathophysiological processes of several diseases such as atherosclerosis,hypertension,chronic kidney disease,stroke,diabetes and cancer,and is regarded as a novel cardiovascular risk factor.Dimethylarginine dimethylaminohydrolases(DDAH) are enzymes responsible for inactivation of ADMA.A decrease in DDAH activity may lead to ADMA accumulation and thus promotes the development of ADMA-related diseases.Recent development in tissue distribution,biological function,regulation of DDAH,and implication of DDAH in human diseases are reviewed presently.