Cathodic and anodic polarization behaviour of SS347 in mixture of highly concentrated phosphoric and acetic acid in the presence of various amounts of dimethyl 2-(2-hydroxyphenyl amino)-3-(tri phenylPhosphoranylidene) butanedioate (L-OH) at different temperatures (20, 30, 40, 50 +/- 1 degrees C) have been investigated potentiodynamically. The cathodic and anodic Tafel slopes values calculated from the polarization curves indicate that the corrosion rate decreases with increasing L-OH concentration. The corrosion potential (E-corr) and passive potential (E-p) increased (shifted slightly toward positive potential) while corrosion current density (I-corr) and passivation current (I-p) decreased with increasing L-OH amount. Critical potential for passivity (E-cr) did not show an remarkable change but critical current density (I-cr) often decreased with increasing L- OH concentration. Maximum inhibition efficiency (95%) is obtained for the alloy in acid solution containing 60 ppm of L-OH The open Circuit potential after polarization attained positive value indicating formation of passive film on the surface of experimental sample. Activation energy (E-a) and Gibbs free energy (Delta G(ads)) for adsorption of L-OH are calculated. The values of Delta G(ads) decreased (attained more negative values) with increasing temperatures.