Abstract We examined sodium selenite, an inorganic selenium supplement, for its ulcer healing properties and antimicrobial activity against gastric pathogen Helicobacter pylori. Minimum inhibitory concentrations (MIC) were determined using disk diffusion and flow cytometry. The studies were performed over a concentration range of 1 microg/ml to 500 microg/ml sodium selenite. Mild activity was seen at 10 microg/ml and 50 microg/ml, a moderate response at 100 microg/ml and strong response at 500 microg/ml with a MIC value of 10 microg/ml. The compound was found to be active at low pH without any resistance after 10 passages. Flow cytometry data showed a characteristic shift of the viability peak in comparison with the control, thereby confirming the bactericidal effects of sodium selenite. Sodium selenite administered in Wistar rats, pre-ulcerated with naproxen and infected with H. pylori, showed ulcer healing and anti-H. pylori activity at a concentration range of 10-50 microg/rat; however concentrations of 100 microg/rat and 500 microg/rat were found to be toxic in the in vivo studies. In conclusion, sodium selenite shows both ulcer healing and anti-H. pylori activity at a low concentration (10 microg/rat) without toxicity.