The aim of the present study was to measure the apparent absorption of magnesium (Mg) originating from Mg-butyrate. Six mid-lactation Holstein Friesian dairy cows were used with dietary treatments arranged in a cross-over design. Two different diets were fed during the experiment, consisting of a low Mg diet without Mg-butyrate (L-Mg, 3.1g Mg/kg dry matter) or a high Mg diet with Mg-butyrate (H-Mg, 3.9 g Mg/kg dry matter). Cows offered the L-Mg diet ingested 54.7 g Mg/day while the cows fed the H-Mg diets ingested 66.3 g Mg/day (P < 0.001). The fecal excretion of Mg, however, was similar between the two experimental diets (P = 0.174). Consequently, apparent Mg absorption was found to be 7.9 percentage units greater (P = 0.038) when the cows were fed the diet supplemented with Mg-butyrate. The greater Mg absorption after feeding the H-Mg diet was, however, not reflected by a greater urinary Mg concentration (P = 0.228). These results indicate that the availability of Mg from the Mg-butyrate supplemented diet is high (34.1% of intake). The fractional Mg absorption from Mg-butyrate was calculated to be 71.6%. In conclusion, Mg-butyrate is an attractive alternative to supplement dairy rations with Mg.