The electrochemical behaviour of plasma-sprayed SS41 steels with The Al2O3-TiO2 system. Cr2O3 and ZrO2 stabilized by Y2O3 ceramics was studied using a potenliostat by measuring Iheir natural potential und anodic polarization curves in 3.5%, NaCI aqueous solution Fhe natulal patential of ceramic-sprayed SS41 steels is tile sa me as tha t olthe stlbstrat. TIle anodie polarization bchaviour of ceramic-sprayed SS4 slecls is also dominaIed by Ibe subslratc through connected porosity. However, the polarizatian current density of ceramic sprayed SS41 steel is lower than that of the substrate because tile current densdy is conlrolled greally by Ihe anlotlllt ptrosity il1 the coating. The connected pt~rosity of ceramic coatings was L}blained quantitatively The polarlzation currenl density ratio between the ceramic-sprayed specinlcn and lhe substratc at Ihe carrcsponding polarization potentkd, The slrong rekltion between the ctmnected portlsily and the porosity of cross-sections of the ceramic coatings, shown using micrographs, was recognized By measuring electrochemically the connected porosity ill coalings obtained under various spraying conditions, it would bc possible to select the oplirnum spraying condibons Io spray coatings which have less porosity.