The so-called Oxide/Metal/Oxide sandwich method is one of the technique used to investigate the dynamic oxidation of metals which happens during the casting process. In this study, characteristics of the oxide films formed on the molten magnesium in dynamic conditions have been investigated using the aforementioned method. The air bubbles were released into the cast sample at the pressure of 0.2 atm through a quartz tube of 1 mm internal diameter. The interface of two adjacent entrapped bubbles is considered as the Oxide/Metal/Oxide (OMO) sandwich. The sandwiches were characterized by the aid of the optical and scanning electron microscopy and also X-Ray diffraction analyses. Two different approaches, including measuring the width of the folds formed on the oxide films and the edge of the sandwiches, were used to estimate the thickness of the films. The thicknesses were estimated to be in the range of 200 to 800 nm. The features such as fold, wrinkle, and crack were observed on the OMO sandwiches. On the microscopic scale, the oxide films were rough and porous. This is attributed to the non-protective behavior of oxide films. The XRD patterns indicated that the oxide films formed on the pure molten magnesium in dynamic conditions are crystallized MgO.