Magnesium (Mg) has been known to play vital roles in regulating growth and various metabolic processes. In recent years, the association between Mg and tumorigenesis has raised more and more attention. However, the effects of Mg on the progression of head and neck carcinoma (HNC), as well as the mechanism behind it, remain undefined. In this study, the roles of Mg in tumorigenic activities were tested in CAL27 and FaDu cells as well as in a xenograft tumor model in nude mice. We demonstrated that a moderate increase in extracellular Mg contributed to the proliferation, migration, and invasion of 2 HNC cell lines, while the addition of Mg in drinking water promoted the growth of xenograft tumors in mice without altering their serum Mg levels. Moreover, TRPM7, a major Mg transporter, was shown to be essential for the tumorigenic activities of HNC and the Mg-induced promotive effects on HNC cells and was further shown to be associated with the activation of AKT/mTOR (mammalian target of rapamycin) signaling. In a preliminary clinical study, we determined the Mg ion concentrations in the stimulated saliva from 72 patients with nasopharynx carcinoma and 12 healthy individuals. Our data revealed that the salivary Mg levels of subjects with nasopharynx carcinoma were significantly higher than those of the healthy controls. This is correlated with our finding showing TRPM7 to be overexpressed in tumor tissues harvested from 9 patients with HNC. Therefore, we can conclude that salivary Mg level, within a certain range, could act as a risk factor for the progression of HNC, which involves the activation of AKT/mTOR signaling pathways through the TRPM7 channel. The control of salivary Mg level and the intervention of TRPM7 should not be ignored during the study of HNC.