Magnesium has three stable isotopes: 24Mg,25Mg and 26Mg. Available data show that the largest Mg-isotopic variation occurs in meteorites, with δ26Mg values of -0.71‰ ～ 11.92‰ (relative to DSM3 standard), whereas the terrestrial rocks show smaller Mg-isotopic variation. For example, mantle rocks show a δ26Mg variation of -3.01‰～1.03‰; sedimentary carbonates display a δ26Mg variation from -4.84‰ to -1.09‰; and loess has a δ26Mg value of -0.60‰. At present, many laboratories use MC-ICPMS for the precise measurement of Mg-isotopic composition. Because of the isotopic heterogeneity of the standard SRM980 produced by NIST, the new standard DSM3 has been recommended as the reference material to report Mg-isotopic compositions. At present the research on magnesium isotope geochemistry is focusing on the following aspects: ① cosmochemistry and star formation processes; ② tracing mantle metasomatism; ③ variation of seawater δ26Mg value through geologic history; ④ estimates of the Mg flux during continental weathering. Study on Mg-isotope geochemistry in China is just starting and the application of Mg isotopes to solving various geological problems will be enhanced in the near future both at home and abroad. 