The inhibiting ability of the fruiting bodies of Melia azedarach Linn extract (FB-MAL) and its synergistic e ff ect with nickel ions (Ni 2+ ) on the corrosion of carbon (C)-steel in hydrochloric acid were investigated using gravimetric measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The FB-MAL inhibited C-steel corrosion in acidic media up to 76.5%. Combining the FB-MAL with Ni 2+ enhanced the adsorption capability of FB-MAL, greatly and consequently increased its inhibitive e ff ect. Potentiodynamic polarization studies revealed that FB-MAL and FB-MAL + 100 ppm Ni 2+ behave as mixed-type inhibitors. The EIS spectra showed that the charge transfer controls the corrosion process. The studied system obeys the Langmuir adsorption isotherm. The kinetic parameters were computed and are discussed later in this paper. The formation of the protective fi lm was con fi rmed using Fourier transform-infrared spectroscopy, UV-Visible spectroscopy and scanning electron microscopy.