Sandwich structures are extensively utilized as a structural component in different engineering applications such as aircraft, automotive and construction industries. For this reason, vibration damping behavior comes into prominence for structural health. Shear thickening fluid (STF) is a candidate smart material for vibration isolation in structural members due to its viscoelastic properties. In this work, we fabricated a novel concept by filling an STF into the extruded polystyrene (XPS) foam core of an aluminum face sheet sandwich structure to take advantage of STF rheology during vibrational loadings. In addition to consideration of temperature effect on STF based structures for the first time, STF usage has been extended to foam core sandwich systems with this design. The vibrational characteristics in these smart composites were analyzed by using modal analysis and therefore, natural frequencies and damping ratios were calculated for the structures. According to the results, STF inclusion in the sandwich structures leads to a significant development in the vibration attenuation properties whereas increasing temperature exhibits a disruption in the damping behavior.