Magnesium ion (Mg²⁺) is an essential divalent cation, and intracellular Mg²⁺ concentration is tightly controlled by various Mg²⁺ transporters. Therefore, Mg²⁺ transporter dysfunction may consequently lead to a variety of diseases, such as cardiovascular, neuronal, and muscular diseases. Recently, several candidate genes for Mg²⁺ transporters have been identified. However, the regulation mechanisms of Mg²⁺ homeostasis are mostly unknown. To clarify these issues, we focused on Mg²⁺-permeable non-selective cation channel TRPM7, and generated kidney-specific transgenic mouse model overexpressing the dominant negative TRPM7 mutant (M7DN-Tg), as an experimental tool. We confirmed that TRPM7 currents in HEK293 cells were almost completely inhibited by co-expression of the M7DN construct. We found that M7DN-Tg exhibited dysregulation of serum Mg²⁺ level and urinary Mg²⁺ excretion. Interestingly, vascular contractile responses in M7DN-Tg were significantly attenuated compared to the responses in wild-type mice. In M7DN-Tg, Mg²⁺-enriched diet recovered the abnormal responses to the normal level. These results suggest that TRPM7 is involved in the　regulation of Mg²⁺ homeostasis. M7DN-Tg will be a useful animal model for studying magnesium disorders.