Molecular hydrogen, as an emerging medical therapeutic gas with small molecular mass and reductivity, recently has been found to have significant therapeutic effects in a variety of cardiovascular and cerebrovascular diseases, such as myocardial ischemia-reperfusion injury, heart failure, atherosclerosis, stroke, hypertension et cetera. Molecular hydrogen can intervene in the progression of cardiovascular and cerebrovascular diseases through preventing oxidant stress, inflammation, apoptosis and regulation of metabolism. This paper reviews the therapeutic role and molecular mechanisms of molecular hydrogen in cardiovascular and cerebrovascular diseases to provide new ideas for the treatments of cardiovascular and cerebrovascular diseases.