The effect of P-providing components (phosphorous acid, H3PO3 and sodium hypophosphite, NaH2PO2) in modified Watts electrolyte (pH = 2; 80 degrees C) on the barrier ability and durability of the deposited Ni-Co-P and Ni-Co (as a reference) coatings during extended exposure in 3.5% NaCl until 672 h was studied. The data acquired for the charge transfer and polarization resistances (R-ct and R-p) by electrochemical impedance spectroscopy, EIS and linear voltammetry, LVA, undoubtedly reveal that the best corrosion protective properties belong to the Ni-Co-P coating deposited at simultaneous occurrence of H3PO3 and NaH2PO2. It was followed subsequently by those obtained from electrolyte with only NaH2PO2, then, deposited from electrolyte with only H3PO3 and finally by the reference Ni-Co coating. The occurrence of an amorphous phase in the structure of Ni-Co-P coatings, combined with the increase of cobalt content and reducing that of nickel, predetermines the best protective properties of the investigated alloys. The established anomalous R-ct and it R-p increment during the exposure of Ni-Co-P coatings could be related to corrosion products accumulation, most probably of metal phosphates, and it forms a barrier layer between the coating and the corrosive medium.