Abstract: The effect of slags on the oxygen probes with ZrO₂ (MgO) solid electrolyte tube was studied. The attack of pure liquid FexO on the ZrO₂ (MgO) tube was sensitive, and it became intenser as the temperature increased. The attack of basic complex slags on the ZrO₂ (MgO) tube was slighter than that of pure liquid FexO, and the attack phenomenon was not marked within 30 min. The ZrO₂(MgO) tube reacted with slag to form calcium zirconic acid on the interface of the tube and the slag, which caused the achieving equilibrium time of the cell EMF to prolong and even to be failure.