Metal foam was produced by the Melt Foaming Method. In this foaming process, the surface tension and the viscosity of molten Al (recycled waste Al) and Mg alloy (Az91) that were measured respectively by the ring method and the rotational method are the most important two factors. They surface tension and the viscosity were investigated in the temperature range of about 600-900°C and the effects of the additional surface-active elements were investigated at the about 640°C. The measured surface tension of the molten recycled Al and Az91 decreased linearly with the increasing temperature of Ar gas (99.999%) and SF6+CO2 (1:100) atmosphere. The effect of surface-active elements is a decrease of the surface tension and an increase of the viscosity. The optimal conditions for the foam metal manufacturing are needed the low surface tension and the high viscosity. It is possible that the optimal conditions of the surface tension and the viscosity can be obtained through controlling the amount of adding surface-active elements.