Abstract: MELAS syndrome (mitochondrial myopathy encephalophathy with lactic acidosis and stroke-like episodes), as one of the most common diseases in mitochondrial encephalomyopathies, is characterized by highly variable manifestations. So, more and more people come to realize the importance of molecular basis of MELAS. This review took the commonest mtDNA point mutation (A3243G) for example to overview its molecular biological mechanism, test strategy and recent progress of study on MELAS syndrome.