Non-substituted or mono-substituted 11-cyano or 11-thiocyanato undecanoic acid phenylamide derivatives were synthesized and characterized with their FT-IR and H-1-NMR spectra. Thereafter, their corrosion prevention efficiencies were investigated. All compounds were tested with steel coupons in acidic medium by a gravimetric method. Acidic tests were done with a medium concentration of 2 M HCl for 5 h at variable temperatures and inhibitor concentrations. The corrosion prevention efficiencies of the inhibitors were compared according to their chemical structures and the corrosion inhibition mechanism was also discussed. The synthesized compounds showed promising corrosion inhibition efficiencies under the outlined test conditions. Best inhibitions were obtained at 27 degrees C and 100 ppm concentration of corrosion inhibitors.