The interest in organoselenium biochemistry and pharmacology has increased in the last two decades due to a variety of organoselenium compounds that possess biological activity. Recently, our group has reported that diphenyl diselenide, a simple diaryl diselenide, is active as a glutathione peroxidase mimic and is a safety drug when administered subcutaneously to mice at doses that have anti-inflammatory and antinociceptive activities. In addition, report demonstrated that the toxicity of diphenyl diselenide depends on the route of administration as well as the species. In fact, diphenyl diselenide administered by i.p. route was more toxic than by s.c route in mice. Therefore, the aim of the present study was to evaluate diphenyl diselenide acute toxicity in mice an rats using oral route of administration with the purpose of offering safety in the use of this compound. To investigate potential toxicity of diphenyl diselenide, mice (25 – 35 g) and rats (180 – 250 g) received a single oral dose of diphenyl diselenide (7.8 - 312 mg/Kg) or vehicle (10mL/ Kg; canola oil) and were observed up to 72 h to determine the lethal potential of diphenyl diselenide (LD₅₀). After 72 h of exposure, animals were slightly anesthetized for blood collection and plasma was obtained and used for biochemical assays. In the present study, we found that LD₅₀ for diphenyl diselenide administered by oral route in mice and rats were estimated to be > 312 mg/Kg (or 1 mmol/Kg) and 312 mg/Kg (or 1 mmol/Kg), respectively. Diphenyl diselenide (7.8 –312 mg/Kg) did not cause mortality in mice, whereas in rats it was observed mortality after exposure of diphenyl diselenide at doses of 156, 234 and 312 mg/Kg. Diphenyl diselenide also caused a reduction in the body weight gain in mice and rats after 72 h of exposure. Moreover, oral administration of diphenyl diselenide in mice and rats, at all doses tested, did not change plasma AST (aspartate aminotransferase) and ALT (alanine aminotransferase) activities, as well as, urea and creatinine levels. In conclusion, our results indicate that diphenyl diselenide is a safety drug, which presents minor toxic effects when administered by p.o route in mice and rats.