Magnesium is an essential metal but few selective transporters have been identified at the molecular level. Microarray analysis was used to identify two similar transcripts that are upregulated with low extracellular Mg²⁺. The corresponding cDNAs encode protein of 131 and 123 amino acids with two predicted transmembrane domains (TMDs). The two separate gene products comprise this family that we have termed MMgT for Membrane Mg²⁺ Transporter because the proteins reside in the membrane and mediate Mg²⁺ transport. When expressed in Xenopus oocytes, MMgT1 and MMgT2 mediate Mg²⁺ transport as determined with two-electrode voltage-clamp analysis and fluorescence measurements. Transport is saturable Mg²⁺ uptake with Michaelis constants of 1.47 ± 0.17 mM and 0.58 ± 0.07mM, respectively. Real-time RT-PCR demonstrated that MMgT mRNA are present in a wide variety of cells. Subcellular localization with immunohistochemistry determined that the MMgT1-HA and MMgT2-V5 fusion proteins reside in the Golgi complex and post-Golgi vesicles including the early endosomes in COS-7 cells. Interestingly, MMgT1-HA and MMgT2-V5 were found in separate populations of post-Golgi vesicles. MMgT1 and MMgT2 mRNA increased by about 3-fold, respectively, in kidney epithelial cells cultured in low magnesium media relative to normal media and in kidney cortex of mice maintained on low magnesium diets compared to those animals consuming normal diets. With the increase in transcripts there was an apparent increase in MMgT1 and MMgT2 protein in the Golgi and post-Golgi vesicles. These studies suggest that MMgT proteins may provide regulated pathways for Mg²⁺ transport in the Golgi and post-Golgi organelles of epithelial-derived cells.