In order to understand alloying effects on the corrosion resistance of Ti-(10$sim$20)%Zr-(2$sim$8%)Nb-0.2%Pd alloys, Polarization curves were measured at 5%HCI solution. The results were interpreted in terms of two parameters obtained by the molecular orbital calculation ; one is the bond order($B_{circ}$) and the other is the metal d-orbital level($M_{d}$). $B_{circ}$ is a measure of the strength of covalent bonds between titanium and alloying elements. $M_{d}$ is correlative with the electronegativity of elements. It was found that increasing of Zr and Nb with higher $B_{circ}$ values showed a lower critical anodic current density in the polarization curve and hence higher corrosion resistance. On the other hand, increasing of Zr and Nb with higher $M_{d}$ values showed a higher corrosion resistance.