Effective antimicrobial compounds are necessary due to increased resistance of antibiotics against microorganisms causing infectious diseases. In this study, imidazolium-TFSI salt [ITFSI: octyl-bis(3-methylimidazolium)-di(bis(trifluoromethane)sulfonimide)] was labeled with I-131 with high efficiency. In vitro uptake experiments of I-131-ITFSI showed high uptake in gram-positive Staphylococcus aureus bacteria. I-131-ITFSI was also evaluated for comparison between bacterial infection and sterile inflammation by in vivo studies. The biodistribution results revealed that I-131-ITFSI might be used as a nuclear imaging agent for detection of bacterial infection.