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Magnesium isotopic compositions are reported for twenty-four international geological reference materials including igneous, metamorphic and sedimentary rocks, as well as phlogopite and serpentine minerals. The longterm reproducibility of Mg isotopic determination, based on 4-year analyses of olivine and seawater samples, was ≤ 0.07‰ (2s) for d 26 Mg and ≤ 0.05‰ (2s) for d 25 Mg. Accuracy was tested by analysis of synthetic reference materials down to the quoted long-term reproducibility. This comprehensive dataset, plus seawater data produced in the same laboratory, serves as a reference for quality assurance and inter-laboratory comparison of high-precision Mg isotopic data.Significant advances have been made on Mg isotope geochemistry over the past decade. It was debated whether or not the Earth has a chondritic Mg isotopic composition. The most recent studies indicate that the Earth, as well as the Moon, have Mg isotopic composition similar to chondrites within 0.07‰ (2s) in 26 Mg/ 24 Mg ratio (Teng et al.