In this paper, the free vibration analyses of aluminum-foam sandwich structures were completed numerically. Foam and aluminum (Al) were used for the core and surface layers of the sandwich structure, respectively. In addition, an adhesive was used as a thin film. Natural frequencies and mode shapes of the sandwich structure were obtained for different thickness core and surface materials. For this, three different sandwich structures, different thickness of the core with same surface layers and the same core thickness with different surface layers thickness, were modeled as SS1, SS2 and SS3. Analyses were performed by ABAQUS/Standard finite element software. The increase in the thickness of the Al layer generally caused a decrease in the frequency, but this decrease is not very dramatic. The increase in the thickness of the core has caused a serious increase in the frequency of the sandwich structure.