Purpose <p>This study extends a fifth order shear deformation theory (FOSDT) for kinematic modeling of the free vibration of various types of functionally graded material (FGM) sandwich plates including single-layer FGM, non-symmetrical and symmetrical FGM sandwich plates.</p> Method <p>This extension is made possible by introducing a unified general formulation that offers a flexibility in choosing from a large range of higher order shear deformation theories for a comprehensive analysis.</p> Results <p>A numerical comparative study of FOSDT with other kinematic theories from literature, all obtained from the unified model, as well as with the three-dimensional (3D) elasticity model was carried out when evaluating the non-dimensional frequency.</p> Conclusion <p>These comparisons demonstrated that the FOSDT produces results that are most similar to the 3D model, suggesting that it is more accurate than other theories; this improved precision is attributed to the model’s ability to capture transverse shear and normal deformations without the requirement for shear correction factors, setting it opposed to lower-order approaches. Furthermore, this study is supplemented by a parametric analysis exploring the effects of material parameters, slenderness ratios, and aspect ratios on the non-dimensional fundamental frequency of FGM sandwich plates across various configurations.</p>