An iron(II) oxalate dihydrate passive interphase was electrodeposited on steel substrate from aqueous oxalate solutions prior to the electrochemical polymerization of pyrrole. The effect of electrochemical process parameters on the morphology and structure of the passive interphase was systematically investigated by scanning electron microscopy(SEM) and X-ray diffractometry (XRD). Our results reveal that the passive interphase is composed of a monolayer of closely packed crystals. The size of the crystals is dependent on the experimental conditions. The iron(II) oxalate dihydrate interphase formed on steel by electrochemical deposition has an orthorhombic structure irrespective of the reaction condition. The unit cell dimensions of the passive interphase formed by electrodeposition are slightly different from those formed by conventional chemical process.