Abstract: Characteristics of molten metal heated with microwaves were the focus of this study. A series of experiments on the direct microwave heating of molten copper and molten iron were conducted in a MobileLab-W-R microwave workstation; both metals were effectively heated by direct microwaves. Effects of indirect versus direct heating were comparatively analyzed using different types of heating chambers. The direct heating method was then further investigated, taking microwave power, mass of molten metal, and temperature into consideration. The mechanism of direct microwave heating of molten metal was discussed. The results show that microwave can directly heat molten iron and molten copper at high rates that increase linearly with increasing microwave power. Heating rates of molten iron are similar to those of molten copper at constant mass and microwave power. However, the mass of molten iron has no clear linear relationship with heating rates due to the involvement of other factors, such as surface area of the molten iron and distribution of the microwaves. According to the theoretical analysis, when the states of copper and iron are transferred from solid to liquid, their resistivities increase, but their permeabilities drop significantly. As a result, the skin effect depths of microwave in molten copper and iron are clearly larger than those in the solid metals. Conductivity loss is the main mechanism of achieving direct microwave heating of molten metal. Microwave energy can be absorbed in four ways: collisions between electrons and nucleus, rapid liquid surface renewal, hindering of internal defects of electron movement, and atom movement and collision. Absorbed microwave energy can be transferred into the internal energy of the molten metal.