Metal foam was produced by the Melt Foaming Method. In this foaming process, the two most important factors were the surface tension and the viscosity of molten Al-Si alloy and AZ91 Mg alloy that were measured, respectively, by the ring method and the rotational method. The surface tension and the viscosities were investigated in the temperature range from melting point to 800 degrees C, and the effects of the added thickening elements were investigated at the mixing temperature. The optimal conditions for the metal foam manufacturing require low surface tension and high viscosity. It is possible that the optimal conditions of the surface tension and the viscosity can be obtained through controlling the amount of added thickening elements and holding temperature.