Sodium tetraborate (Na2B4O7) has been widely used as an electrolyte and pH buffer in studying the interfacial electrochemistry of sulfide minerals in relation to sulfide mineral flotation, In all the previous studies published so far, berate was regarded as an inert electrolyte/pH buffer, and its reactions with the sulfide minerals were completely overlooked. In this first part of this series papers, the complicating effects of berate on the interfacial electrochemistry of pyrite have been studied. It has been demonstrated that berate is not an inert electrolyte/pH buffer. It strongly reacts with the surfaces of pyrite. In the berate solutions, the surface oxidation of pyrite is strongly enhanced. The first and rate-determining step of the reaction between berate and pyrite has been shown to be the following irreversible reaction : FeS2 + B(OH)(4)(-) double right arrow FeS2 ...[B(OH)(4)](ads) + e. This reaction appears in the voltammogram as an anodic oxidation peak at potentials of more than 0.4 V lower than the commencement of pyrite oxidation in sodium perchlorate or nitrate electrolyte solutions, As the berate concentration increases, the peak current increases linearly, while the peak potential shifts positively at 240 mV per decade. On a rotating-disc electrode, the peak becomes a plateau. The limiting current density is a linear function of the square root of the rotation speed at relatively low rotation speeds, The Tafel slope, i.e., dE/d{log I}, is close to 240 mV per decade and is independent of the rotation speed and berate concentration, The results indicate that charge transfer coefficient (alpha) is 0.25.