Abstract: Based on experimental results, it shows that the foaming behaviours occurred in metallurgical melts is similar to that taken place in aqueous solution. There are two types of foam structure, spherical foam and polyhedral foam, in the bath-smelting processes and the foaming process of Al alloy melt. Foams with large bubbles, generated by argon gas injection into liquid slag with a mon-orifice nozzle, have polyhedral bubble cells and the foamability of slag is affected by the gas injection rate and container scale besides the surface tension and the viscosity of slag. Foams with fine bubbles, generated by slag/metal interfacial reaction in the bath-smelting prcx^ess or the decomposition of TiH₂ in molten Al alloy, have spherical bubble cells in the initial foaming stage and the translation from spherical bubble structure into polyhedral bubble structure takes place at the end of foaming process. Under conditions of gas evolution due to chemical reaction in melts, the foam stability is strongly affected by the rate of gas evolution, the size of bubbles and the fluid flow form besides the physico-chemicaJ properties of melts.