Foamed metal is a kind of porous material with pores in the metal matrix. One of the possible process routes is to blow gas bubbles into liquid metals. However, many metallic foams produced by this foaming method have coarse and irregular cell structures. The industrial aim is to fabricate foams with more uniform structure and cell size. It is important to understand the mechanisms and factors controlling. The rheological characteristics are the most important factors in the metal foam manufacturing. Thus this study investigated the bubble behavior of the molten metal and its two most important two parameters: surface tension and liquid viscosity. The surface tension (by the ring method) and the viscosity (by the rotation method) of Mg-Al alloy (AZ91, AM60) have been measured under pure Ar and SF6 + CO2 atmosphere. The results show that the surface tension and the viscosity of these alloys decrease with increasing temperature. The addition of Ca and SiC to Mg alloys decreases the surface tension and increases the viscosity. This anomalous behavior is related with the preferential adsorption of high activity elements on the surface.