Magnesium is a ancient cation but it can be used successfully as adjuvant to Local anaesthetic agent.iIt can be used successfully in various Surgeries like neurosurgery, cardiac surgery,as induced hypotensive agent,in FESS Surgeries, used for attenuation of pressure response to laryngoscopy& intubation,also to prevent postoperative sore throat.It can be used in critical care,& in obstetrics to prevent Eclampsia.In present article various uses of Magnesium sulfate discussed. Introduction Magnesium is the second most abundant intracellular cation1,2 and the fourth when the extracellular medium is also considered1. It is involved biological reactions, such as3: hormone binding to receptors, flow of trans-membrane ions, regulation of the adenylate kinase system, muscle contraction, neuronal activity, vasomotor tone, cardiac excitability, release of neurotransmitters, and calcium binding to calcium channels. In 1906, Haulbold and Meltzer reported sensorial and mo-tor blockades in humans after the intrathecal administration of magnesium; in 1950, magnesium was used in anesthesia, mainly to control seizures in gravidas. Currently, it has several applications in anesthesia, obstetrics, and critical care3-5. The objective of present review was to access the physiology, pharmacology, and reduction in plasma levels of magnesium, as well as some of its applications in obstetrics, anesthesia, analgesia,& critical care