This research includes results on the electrochemical performance of carbon steel in cement-based mortar when Opuntia Ficus Indica (OFI) slime was used as an addition in the mortar water mixture. Two were the OFI slimes used: cooked and exudate. The cooked OFI slime was produced from boiling cladodes with water in a 1:1 mass ratio, during 1 hour. The exudate OFI slime was extracted by placing OFI cladodes in water, same 1:1 ratio, during 48 hours. The OFI slime addition was mixed at different concentrations (4%, 8%, 15%, and 30% by water content). Half-cell potentials (E) and linear polarization resistance (LPR) measurements were performed at different time periods to characterize the possible corrosion inhibiting effect of the tested addition concentrations. Results showed better corrosion inhibiting effect of the cooked OFI slime for carbon steel, as compared with exudate OFI slime additions.