Abstract The electrochemical behavior and compositions of passive films formed on the constituent phases (α-phase, γ-phase) of 2205 duplex stainless steel (DSS) without coupling in neutral 3.5% NaCl solution were investigated, utilizing single-phase samples prepared by selective dissolution. The results demonstrate that, compared to γ-phase, Fe species in passive film of α-phase are more stable due to the higher content of Mo within α-phase. The superior stability of Cr (III) species in the passive layer of γ-phase may result from the higher content of Ni in γ-phase, which leads to the higher content of Cr, Cr/Fe ratio, and better passivity of passive layer. The beneficial effect of coupling of two phases on the passive behavior of 2205 DSS is also found.