Résumé : Published data on the bioavailability of various Mg preparations is too fragmented and scanty to inform proper choice of Mg preparation for clinical studies. In this study, the relative bioavailability of three preparations of Mg (amino‐acid chelate, citrate and oxide) were compared at a daily dose of 300 mg of elemental Mg in 46 healthy individuals. The study was a randomised, double‐blind, placebo‐controlled, parallel intervention, of 60 days duration. Urine, blood and saliva samples were taken at baseline, 24 h after the first Mg supplement was taken (acute‘ supplementation) and after 60 days of daily Mg consumption (chronic‘ supplementation). Results showed that supplementation of the organic forms of Mg (citrate and amino‐acid chelate) showed greater absorption (P ∓ 0.033) at 60 days than MgO, as assessed by the 24‐h urinary Mg excretion. Mg citrate led to the greatest mean serum Mg concentration compared with other treatments following both acute (P ∓ 0.026) and chronic (P ∓ 0.006) supplementation. Furthermore, although mean erythrocyte Mg concentration showed no differences among groups, chronic Mg citrate supplementation resulted in the greatest (P ∓ 0.027) mean salivary Mg concentration compared with all other treatments. Mg oxide supplementation resulted in no differences compared to placebo. We conclude that a daily supplementation with Mg citrate shows superior bioavailability after 60 days of treatment when compared with other treatments studied.