The corrosion inhibition of carbon steel in 1.0 M hydrochloric acid solution in the presence of some phenolic compounds such as o-aminophenol, catechol, salicaldehyde and salicylic acid was investigated using weight-loss method ,potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Results obtained showed that the inhibition efficiency of these compounds increased by increasing their concentration but decreases with a rise in temperature. The effect of the investigated compounds and KI, KSCN and KBr has also been studied. The apparent activation energy (Ea) and other thermodynamic parameters for the corrosion process have also been calculated. The potentiodynamic polarization data indicated that the inhibitors were of mixed-type. The slopes of the cathodic and anodic Tafel lines (βc and βa) are approximately constant and independent of the inhibitor concentration. The adsorption of these compounds on C- steel surface has been found to obey the Freundlich adsorption isotherm. Double layer capacitance, Cdl, and charge transform resistance, Rct, values were derived from Nyquist and Bode plots obtained from A.C. impedance studies. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.