Foaminess and foam life were measured by gas injection into molten slags containing iron oxide. The results obtained in this work are as follows : (1) Foams observed in iron oxide slag melts are essentially unstable, and the foaminess of the slag melts depends on the rate of foaming by gas injection and decay rate of the foams. So the foam height at constant gas flow rate increases with increasing foam life. (2) The foaminess and foam life of the slags increase rapidly by decreasing O/Si ratio of the slags below 3.5. (3) Foam life has a relation to the surface tension of the slags, and the decrease of the surface tension of the slags contributes to the increase of the foam life. (4) Foaminess and foam life with Ar+ 3%H₂ gas are higher than with Ar gas. It can be explained by lowering the coalescing rate of foams caused by reduction of foam size and existance of metal particle on the foam surface during the injection of the gas containing hygrogen. (5) Addition of P₂O₅, Na₂O or CaF₂ to the FeO-CaO-SiO₂ slags contributes to increase in the foaminess and foam life. It may be shown that the Maragoni effect is responsible for the increase in foam stability by those additions. While the addition of MgO has no effect on foam stability.