Selenium concentration and bioavailability were assessed in a common Mato Grosso urban regional diet (RUDMT), using 52 Wistar male weanling rats, weighing 56.2±1.4 g. Thirty-two rats were fed a casein diet that was free of selenium, vitamin E and methionine and contained anti-oxidant-free oil for a 30 day period in order to induce a selenium deficiency. The remaining rats were fed on a casein diet, forming control group I, with 0.10μg of selenium per gram of diet. After selenium deficiency had been established, 24 rats were divided into three groups which were fed on three different diets for 25 days: (i) RUDMT group, with 0.02μg of selenium per gram of diet; (ii) control group II, with 0.10μg of selenium per gram of diet; and (iii) pair-feeding group, with 0.04μg of selenium per gram of diet. During this latter period, the control group I without depletion continued to be fed on the casein diet with 0.10μg of selenium per gram of diet. Apparent selenium absorption, selenium concentration and the enzymatic activity of the glutathione peroxidase (GSH Px) in plasma, liver and kidney were determined in order to assess the selenium bioavailability. The RUDMT group showed low selenium bioavailability than the control groups. The low concentration of selenium and other components in the RUDMT diet might have contributed to this result.