When the melt is in the nonprotective atmosphere, Oxidation of alloys containing non-noble metals mainly results in a solid film formation on the melt surface. Formation of the film either in the melting stage or in the melt movement stage into the mould, i.e. casting stage is possible. Solid oxide films seem to be one of the main reasons for porosities and they decline the reliability of the castings. In this study, with air blowing into the bulk of melt during pouring process and formation of oxide-metal-oxide sandwich, characteristics of surface oxide films in casting stage by OMO sandwich method have been investigated through SEM and EDS. To form bubbles, air was blown at 0.12 MPa into the melt and with the formation of OMO sandwich between two or more bubbles, process was stopped. Results show that thickness of short time oxide films in ZA27 alloy change in the range of 30-150nm. Possible consequences of the characteristics of the oxide films are discussed.