Abstract Hydrogen sulfide is a corrosive species responsible for the deterioration of metals and alloys in marine environment. In this study, the electrochemical performance of the 90/10 Cu–Ni alloy in stagnant and aerated 3.5% sodium chloride (equivalent chloride concentration in seawater) containing 0.01 M Na2S was investigated using potentiodynamic polarization technique at 23, 50, and 80°C. The surface examination and morphological studies were also employed. Polarization measurements in sulfide-infested environments revealed that 90/10 Cu–Ni alloys are adversely sensitive to the sulfide presence and exhibit very high corrosion rates at higher electrolyte temperatures in accordance with an exponential fashion. In addition, the confirmation of a corrosion attack evidencing a pitting type corrosion appearing after the metallographic characterization was applied.