Methionine synthase reductase (MTRR) is one of the important enzymes involved in the folate metabolic pathway and its functional genetic polymorphisms may be associated with breast cancer risk. MTRR A66G polymorphism is not associated with breast cancer risk, especially in Caucasians and Asians. Methionine synthase reductase (MTRR) is involved in the DNA synthesis and production of S-adenosylmethionine (SAM) and plays an important role in carcinogenesis. MTRR expression, which is increased in human ovarian cancer (OC), is related to the differentiation and cisplatin resistance of OC cells. MTRR silencing inhibits cell growth and cisplatin resistance by regulating caspase expression and mTOR signaling pathway in OC cells. It is suggested that MTRR may be a potential target for the therapy of OC.