A novel chemical sensor for sulfate detection was proposed in this study, utilizing sulfate binding protein (SBP) derived from Escherichia coli as sulfate recognition element. Purified SBP was immobilized on a gold electrode modified with cysteamine and glutaraldehyde. In this study the surface potential change of the SBP modified electrode to sulfate and various ions were investigated. In order to evaluate nonspecific interaction with ionic species, proteins with various isoelectric point were immobilized on the surface of gold electrode and response to ions were measured and compared to sulfate binding protein modified electrode. We made clear that the protein modified electrode shows the potential change to ions and these potential change was effected by the isoelectric point of the protein molecule, and BSA, whose isoelectric point is closest to that of SBP, showed the similar response to ions except sulfate. With use BSA modified electrode as a reference electrode, this sensing system showed selective response to sulfate, probably because of the selective binding sulfate by SBP. This potential change difference between the SBP modified electrode and the BSA modified electrode depended on the concentration of sulfate with in the range of 5 - 150 mM.