Abstract: Inherited metabolic diseases are a group of metabolic disorders caused by singe gene defect. Many of these diseases carry serious clinical consequences to neonate or infant and therefore are a major part of newborn screening. The application of tandem mass spectrometry is the most important renovation in the field besides the application of bacterial inhibition assay to the screening of phenylketonuria by Guthrie. Recently, tandem mass spectrometry has revolutionized the field with rapid progress in technology. This paper reviews the advantages, fundamentals and screening diseases of tandem mass spectrometry. Future of this technology in newborn screening for inherited metabolic diseases is also predicted.