Dense oxygen ion–conducting ceramic membranes with CO2 resistance can promote many advanced applications such as membrane reactors for green chemical synthesis and oxy‐fuel combustion for clean energy delivery. The state‐of‐the‐art perovskite oxide membranes are characterized by their high O2 flux but low stability in a CO2‐containing atmosphere. To solve this problem, dual‐phase membranes have captured the imagination of researchers. Herein, a novel dual‐phase hollow fiber membrane with a composition of 40 wt% Ce0.9Gd0.1O2–δ (GDC)–60 wt% La2NiO4+δ (LNO) is developed via a combined phase inversion sintering process. During the high temperature treatment, La‐doping behavior is observed with La leaching out from the LNO phase and diffusing into the GDC phase. This dual phase membrane displays the O2 flux of 1.47 at 950 °C, which is reduced by 10% to 1.31 mL min−1 cm−2 when the sweep gas is switched from helium to pure CO2. Such minor O2 flux reduction is due to the strong CO2 adsorption on membrane surface occupying the O2 vacancies without permanent membrane damage, which is fully eliminated by an inert gas purge. Such a robust dual‐phase membrane exhibits the potential to overcome the low stability problem under the CO2‐containing atmosphere.